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Soil Moisture Stress Induces Transplant Shock in Stored and Unstored 2 + 0 Douglas-Fir Seedlings of Varying Root Volumes

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Abstract

Transplant shock was induced by applying a range of soil water contents to unstored and cold-stored 2-yr-old (2 + 0) bareroot Douglas-fir seedlings graded by root volume. Moisture stress had the greatest influence on morphological characteristics that express transplant shock. Seedling terminal growth, stem diameter growth, and needle length increased dramatically with increased soil moisture content. In addition, number of needles per centimeter on the terminal greatly increased with increasing moisture stress. Under high moisture stress, seedlings with relatively high root volumes tended to exhibit early reduced growth, but later showed significantly increased overall growth regardless of soil water content. In every case, seedlings grown in the driest soil had the lowest dry weights and those grown in the most moist soil had the highest weights for all seedling components. Similarly, seedlings with the smallest initial root volumes had the lowest dry weights, and those with the largest root volumes had the highest weights. The results indicate that moisture stress is a cause of transplant shock, and that increased seedling root volume may enable seedlings to avoid shock following outplanting to a specific site. FOR. SCI. 39(2):275-294.
Forest Science, Vol 39, No 2, pp 275-294
Soil Moisture Stress Induces
Transplant Shock in Stored and
Unstored 2 + 0 Douglas-Fir Seedlings
of Varying Root Volumes
DIANE L. HAASE
ROBIN ROSE
ABSTRACT. Transplant shock was induced by applying a range of soil water contents to unstored and
cold-stored 2-yr-old (2 + 0) bareroot Douglas-fir seedlings graded by root volume. Mois-
ture stress had the greatest influence on morphological characteristics that express
transplant shock. Seedling terminal growth, stem diameter growth, and needle length
increased dramatically w/th increased soil moisture content. In addition, number of nee-
dles per centimeter on the terminal greatly increased w/th increasing moisture stress.
Under high moisture stress, seedlings w/th relatively high root volumes tended to exhibit
early reduced growth, but later showed significantly increased overall growth regardless
of soil water content. In every case, seedlings grown in the driest soil had the lowest dry
weights and those grown in the most moist soil had the highest weights for all seedling
components. Similarly, seedlings w/th the smallest initial root volumes had the lowest dry
weights, and those w/th the largest root volumes had the highest weights. The results
indicate that moisture stress is a cause of transplant shock, and that increased seedling
root volume may enable seedlings to avoid shock follow/ng outplanting to a specific site.
FOR. Scl. 39(2):275-294.
Pd)DITIONAL KEY WORDS. Drought, seedling quality, nursery grading, planting.
RANSPLANT SHOCK CAN BE A SERIOUS IMPEDIMENT to re?restation efforts. A
seedling in shock is characterized by "bottle brushing symptoms (stunted
terminal growth with shortened needles and a greater number of needles
per unit of leader), browning or loss of needles, cessation of growth, or even
death. A seedling is considered to be in shock until it reaches a growth rate it
would have attained had it not been transplanted (Mullin 1963).
Mullin (1964) and Eis (1966) both found that transplant shock reduces seedling
leader length in white spruce (Picea glauca [Moench] Voss) by about 50% in the
first year after outplanting. Smith and Walters (1963) found similar results in
Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco.). This slow growth, combined
with the stressed condition of a seedling in shock, can result in a longer stand
rotation age and even plantation failure, especially in the presence of competing
vegetation.
Researchers have generally indicated that the root system's ability to take up
water in a new site is an important factor (Mullin 1963, Rietveld 1989). Following
transplanting, a seedling must recover from any damage, reestablish root-to-soil
contact, and resume water and nutrient uptake in a new environment. During this
MAY 1993/275
adjustment period, the seedling continues to transpire, resulting in a stressed
condition of physiological drought (Rietveld 1989). One study suggests that trans-
plant shock primarily results from poor root-to-soil contact after planting, when air
gaps form at the root-soil interface (Sands 1984). Soil drought further contributes
to the stressed condition of the seedling. Katffmann (1977) found that growth of
Monterey pine (Pinus radiata D. Don) seedlings was reduced significantly in dry
soils.
Attempts have been made to increase drought resistance in planted seedlings
by preconditioning with moisture stress (Rook 1973, Unterscheutz et al. 1974,
Kaushal and Aussenac 1989). Although results of these studies indicate that
drought-precondifioned seedlings have lower transpiration rates, transplanted
seedlings still exhibited reduced terminal shoot growth and greater mortality as
compared to undisturbed seediin•s (Kaushal and Aussenac 1989).
Nursery cultural practices such as fertilization, irrigation, root pruning, and
packing have also been examined as factors affecting seedling field performance
(Smith et al. 1966, Melior et al. 1971, Tanaka et al. 1976, Darbyshire 1984,
Jopson and Paul 1984). Stock types have also been researched as determinants in
outplanting success (Grossnickle and Blake 1987, Arnott and Burdett 1988). In
addition, seedling size has been implicated as an important factor in transplant
shock in that survival and growth tend to increase with seedling size (Walters and
Kozak 1965, Dobbs 1976, Zaerr and Lavender 1976). Damage to the root system
during lifting and handling procedures may also be a significant factor (Mullin 1963,
Stoneham and Thoday 1985, DeYoe 1986, Tabbush 1986). Nonetheless, even
seedlings grown under optimum cultural practices and carefully handled are known
to go into shock following transplanting.
Cold storage may influence transplant shock. Survival potential, growth capac-
ity, and field performance of seedlings stressed after storage have been found to
approximate that of unstressed seedlings (Jenkinson and Nelson 1984). Despite
delayed root growth, cold-stored seedlings appear to be better able to avoid
transplant shock and early drought (Blake 1983). On the other hand, Ritchie
(1982) suggests that the depletion of sugars during storage may lead to a reduc-
tion in turgor maintenance, and hence a reduction in drought resistance.
It is unlikely that transplant shock can be entirely eliminated. However, the
ability to identify specific seedling characteristics that are correlated with mini-
mum transplant shock symptoms would be useful. These targeted characteristics
could be used to supplement current seedling grading criteria. Burdett (1983) and
Sutton (1979) both emphasize the importance of a quality grading system which
ensures that stock is well adapted to the planting site.
Douglas-fir, selected for this research, is the most extensively harvested spe-
cies in the Pacific Northwest because of its wide distribution and desirability for
wood products. The relatively narrow midwinter "lifting window" for maximizing
planting stock quality has necessitated large-scale cold storage of tree seedlings.
Therefore, both unstored and stored seedlings were examined in separate ex-
periments, which are here reported together.
Despite the quantitative evidence of the effects of transplant shock, relatively
little research has specifically examined its physiology and morphology, perhaps
because of the difficulty in assessing such a transient problem. No definite cause
of transplant shock has been determined to date. The objective of these studies
was to evaluate the relationship between soil moisture content, initial root vol-
276/FoP'•F•x3cw-NCE
ume, and transplant shock in both cold-stored and unstored 2 + 0 bareroot Doug-
las-fir seedlings in order to link specific causes quantitatively with shock. The null
hypotheses tested were: (1) soil moisture stress does not cause transplant shock,
and (2) transplant shock is not a function of initial seedling root volume over a
given range of moisture regimes.
MATERIALS AND METHODS
PLANT MATERIAL
Two-year-old (2 + 0) bareroot Douglas-fir seedlings from a Bureau of Land Man-
agement northwestern Oregon provenance (seedlot 261-20-01, Western Forest
Tree Seed Council, State of Oregon Tree Seed Zone) were grown under standard
nursery cultural practices at International Paper's Kellogg Nursery located in
western Oregon, approximately 10 km south of Elkton. Seedlings were sown in
May 1988. A live tree count before lifting, on January 18, 1990, gave a density of
25 trees/ft 2, with a mean height of 34.8 cm and a mean stem diameter of 4.5 mm.
Following lifting, seedlings were root pruned to 20.5 cm and graded to oper-
ational specifications at the nursery (height > 20.3 cm and stem diameter > 4
mm). Haft of the seedlings were transplanted ("unstored seedlings") and half were
placed in cold storage (1-2øC) for 130 days prior to transplanting ("stored seed-
lings"). Before transplanting, each tree was measured for height (cm), from
cotyledon scar to base of terminal bud; stem diameter (mm), just below the
cotyledon scar; root volume (cm3), by water displacement (Burdett 1979); and
total fresh weight (g).
TREATMENTS
Following measurement, both unstored and stored seedlings were divided into
four root-volume categories (Table 1), determined from root-volume distributions
(Figure 1). The stored seedlings had slightly smaller root volumes and a wider
range than did the unstored seedlings. As a result, the root-volume categories
differed slightly. Each seedling was then assigned at random to a moisture-stress
treatment (Table 1). The 16 moisture treatment/root volume combinations were
TABLE 1.
The 4 root-volume categories of unstored and stored seedlings and the four
moisture treatments used in transplant shock experiments (16 combinations).
Seedling root
volume (cm a)
Moisture regime
(field capacity = 42%)
Soil water Soil water
Category Unstored Stored Treatment content (%) potential (MPa)
1 5-8 5-7 1 6 - 1.60
2 9-10 8-9 2 12 - 0.80
3 11-13 10-12 3 18 -0.10
4 14-20 13-23 4 24 - 0.01
MAY 1993/277
replicated in 6 blocks. Identical treatments were used for both unstored and
stored seedlings.
Seedlings were transplanted into 15 I plastic pots (5 seedlings per pot) in a
1:2:1:1 (v:v:v:v) sterilized mixture of fine peat:pumice:sand:loam. This mix pro-
vided a deskable soil moisture release curve for a wide range of soil moisture
conditions. Each pot contained the same weight of soil mix. All pots were thor-
oughly watered after planting and placed in a controlled greenhouse environment
at Oregon State University's Forest Research Laboratory. Extended daylength
conditions and day-night temperatures of 30øC and 20øC were maintained through-
out both experiments. Outdoor temperatures often exceeded the capacity of the
greenhouse cooling system during growth of the stored seedlings; therefore,
day-night temperatures were often higher than those that occurred during growth
of the unstored seedlings. Air was circulated for 6 hr daily to encourage seedling
transpiration and better simulate a natural transplant environment.
Moisture-stress treatments were selected on the basis of experimental trials
(Nursery Technology Cooperative, unpublished data), and represent a wide range
of soil water potentials (Table 1). Moisture-stress treatment conditions were
created by watering all pots to field caparty, allowing them to dry to a predeter-
mined soil moisture content, and then rewatering them to field capacity. This
cycle of watering was continued over a period of several weeks.
Pots were weighed 2-3 times per week to assess water content. Weight of
seedlings was considered to be negligible. Soil water content was calculated
according to the following equation:
TW - (DS + P)
WC= DS
where
WC = water content of desired treatment,
TW = total weight (soil + water + pot),
DS = average weight of dry soil in each pot, and
P = weight of pot.
Rearranging the above equation, the weight of each pot at the desired soil water
content was determined as: TW = (WC * DS) + DS + P. As expected, the
mean number of days between waterings differed significantly among moisture-
stress treatments, ranging from an average of 11 to 35 days from the wettest to
dfiest treatments. In addition, the mean number of days between waterings
differed significantly among root-volume categories, ranging from an average of 15
to 21 days from the largest to the smallest root-volume categories.
MEASUREMENTS
The number of days to budbreak was monitored and recorded. Buds were con-
sidered broken when the bud scales first parted, exposing needles. After 60 days,
terminal length and mean lateral length (average of 5 longest laterals) were mea-
sured (for unstored seedlings only). Unstored and stored seedlings were har-
vested 115 days and 95 days, respectively, after transplanting. At the time of
harvest, predawn plant moisture stress (PMS) of one seedling from each pot was
278/FOmS'rSC•CE
measured with a pressure bomb (Scholander et al. 1965, Cleary and Zaerr 1980).
Following harvest, each seedling was measured for the following morphological
parameters: total height (cm); stem diameter (mm); stem diameter growth (mm);
new terminal length (mm); number of buds on the new terminal; needles per
centimeter (mean of 2 cm in middle of termiml); needle length (mean of five
needles from middle of terminal); and number of new laterals. These parameters
were selected because they most commonly exhibit symptoms of transplant shock
either by being indicators of bottle brushing or by being a measure of seedling
quality. In addition, seedlings were divided into root, needle, and stem segments,
and dried for 48 hr at 68øC. Dry weights (g) were then measured for each seedling
component.
EXPERIMENTAL DESIGN
This experiment was arranged in a 4 x 4 factohal, randomized complete block
design. Each of the six benches in the greenhouse was designated as one block
because of temperature gradients and placement of the heating system, light
fixtures, and fans inside the greenhouse. Pots were randomly placed on each
bench and rearranged periodically to reduce possible position effects. Each pot
represents an experimental unit, and each of the five seedlings in a pot is a
sampling unit.
STATISTICAL ANALYSIS
Data were analyzed using analysis of variance (ANOVA) for a randomized com-
plete block design. Tests for normality, iinearity, and constant variance of the
residuals were performed, and transformations were made where necessary to
ensure the validity of these assumptions. Because terminal and lateral length were
measured twice for unstored seedlings, a split-plot analysis with time was done to
determine differences in root-volume category and moisture-stress treatment
effects on growth at the middle and end of the study. Fisher's Protected Least
Significant Difference (FPLSD) procedure was used to determine significant dif-
ferences in data among moisture-stress treatment and root-volume categories at
the a •< 0.05 level. Statistical Analysis System (SAS Institute Inc. 1982) software
was used for analysis of all data. Because unstored and stored seedlings were
studied in separate experiments, they could not be compared statistically. How-
ever, observational differences were noted.
RESULTS
This study was successful in inducing transplant shock. Analyses of experiments
with unstored and stored Douglas-fir seedlings indicate that both moisture-stress
treatment and initial seedling root volume were significant factors affecting most
parameters measured. Sums of squares were much greater for soil moisture
treatment than for root volume on all bottle brushing parameters for both un-
stored and stored seedlings (Table 2). These results indicate that moisture stress
explains the largest proportion of the variance found in the seedling morphological
characteristics that express transplant shock.
1VIAY 1993/279
TABLE 2.
Results of ANOVA for selected growth parameters of unstored and stored
seedlings. (Note: soil water content = SWC; root volume = RV.)
Unstored seedlings Stored seedlings
Source of Degrees of
variation freedom Mean square P Mean square P
Height growth
Block 5 17.82 1041.31
SWC 3 106258.63 0.0001 21056.63 0.0001
RV 3 5289.46 0.0100 7606.24 0.0001
SWC x RV 9 2125.41 0.1222 524.05 0.4919
Error 75 1304.41 554.47
Stem diameter growth
Block 5 1.80 0.749
SWC 3 23.09 0.0001 7.747 0.0001
RV 3 0.35 0.5600 1.663 0.0012
SWC x RV 9 0.28 0.8316 0,302 0.4033
Error 75 0.50 0.285
Needle length
Block 5 59.01 15.00
SWC 3 1052.83 0.0001 241.36 0.0001
RV 3 67.77 0.0458 15.88 0.3564
SWC x RV 9 16.20 0.7341 25.42 0.0917
Error 75 24.22 14.5
Needles/cm
Block 5 0.11 0.12
SWC 3 5.67 0.0001 3.91 0.0001
RV 3 0.26 0.0456 0.12 0.1131
SWC x RV 9 0.06 0.7447 0.10 0.0809
Error 75 0.09 0.06
PRETREATMENT MORPHOLOGY
Root volume and other morphological characteristics are clearly related (Table 3).
Although the range of values for seedling total fresh weight, stem diameter, and
height overlaps among the four root-volume categories, seedlings with larger root
volumes tended to have greater weights, stem diameters, and heights.
Linear regression revealed that root volume is clearly related to seedling
height, weight, and diameter (P = 0.0001). Total fresh weight was most strongly
related to root volume (r 2 = 0.88), which might be expected because total weight
includes the weight of the roots. Stem diameter and root volume were also closely
related (r 2 = 0.72). Height and root volume were significantly, yet poorly, related
(r 2 = 0.07).
BOTTLE BRUSHING AND MOISTURE STRESS
Plant moisture stress before harvest was significantly affected by soil water
content for both unstored (P = 0.0002) and stored (P = 0.0062) seedlings (Table
280/FOP, FXrSC•NCE
TABLE 3.
Initial morphological characteristics of unstored and stored Douglas-fir
seedlings by root-volume category (n = 120).
Unstored seedlings Stored seedlings
Characteristic
by root-volume Standard Standard
category Mean deviation Range Mean deviation Range
Root volume (cm 3)
1 6.93 1.12 5.0-8.0 6.17 0.83 5.0-7.0
2 9.47 0.50 9.0-10.0 8.53 0.50 8.0-9.0
3 12.00 0.85 11.0-13.0 10.96 0.84 10.0-12.0
4 16.18 1.89 14.0-20.0 15.78 2.29 13.0-23.0
Total fresh weight (g)
I 17.57 3.00 11.2-25.8 17.83 3.67 10.2-28.0
2 24.34 3.57 18.0-41.4 23.44 3.29 14.8-32.2
3 28.80 3.99 20.8-40.9 29.52 4.63 18.5-46.9
4 38.63 6.32 27.3-58.2 39.92 6.05 23.4-60.7
Diameter (ram)
1 4.55 0.46 3.2_.•6.0 4.53 0.46 3.5-5.7
2 5.25 0.54 4.1-7.8 5.11 0.50 3.6•5.4
3 5.55 0.48 4.5-7.6 5.65 0.58 4.0-7.5
4 6.32 0.62 4.8-7.8 6.51 0.69 4.9-8.6
Height (cm)
1 32.36 4.09 22.5-42.0 33.17 4.48 21.0-42.5
2 34.73 4.49 20.0-44.0 34.25 4.67 20.5-47.0
3 34.50 4.89 21.0-47.5 36.18 4.80 23.0-46.0
4 36.49 4.55 26.0-47.0 36.74 4.72 22.0-47.0
3). These effects might have been more pronounced if all pots had been at their
assigned level of moisture stress. However, since watering cycles varied consid-
erably with treatment and root volume, that was not possible. In addition, bottle
brushing indicators were significantly influenced by soil water content for both
unstored and stored seedlings (Table 4). Figure 2 reflects the mean values of
bottle brushing parameters for seedlings from low and high soil water content
treatments.
For unstored seedlings, terminal growth was more than doubled between the
6% and the 24% soil water content treatments. Although not quite as dramatic,
the same effect was found in seedlings transplanted following storage, with ter-
minal growth increasing by about 50% between the 6% and the 24% soil water
content treatments. Soil water content also had a profound effect on relative
height growth (cm growth/cm initial height), which approximately doubled for both
unstored and stored seedlings between the lowest and the highest soil water
content treatments.
As with terminal growth, soil moisture content had a significant effect on needle
characteristics. Seedlings grown in the wettest treatment (24% soil water con-
tent) had terminal needles which were 35% and 18% longer (for unstored and
stored seedlings, respectively) than those grown in the driest treatment (6% soil
water content). In addition, number of needles per centimeter on the terminal
greatly increased with increasing moisture stress. Unstored seedlings grown in
the soil with the lowest water content had 60% more needles per centimeter than
MAY 1993/281
80'
70' A
60'
50'
40,
30'
20.
10'
0
80'
70' B
60'
50'
40.
30
20
10'
0, 2
FIGURE 1.
4 6 8 10 12 14 16 18 20 22 24 26
ROOT VOLUME (cm 3)
Root-volume distribution for (A) unstored seedlings and (B) stored seedlings.
28
those grown with the highest water content. Similarly, a 50% increase was found
for seedlings transplanted after storage.
BOTTLE BRUSHING AND ROOT VOLUME
Root volume also had a significant effect on bottle brushing parameters (Table 4).
This effect, however, was not as striking as was that of soil water content. Initial
seedling root volume did not have a significant effect on PMS at the time of
harvest.
The effect of initial seedling root volume on terminal growth changed signifi-
282/FORESTSCIENCE
MAY 1993/283
FIGURE 2. Sketch reflecting mean values of bottle brushing parameters for seedlings with similar
initial root volumes grown in (A) 6% soil water content and (B) 24% soil water content.
canfly between 60 days and 115 days for unstored seedlings. At 60 days, terminal
length stayed relatively constant over all root-volume categories for seedlings
grown under the more moist conditions (18-24% soil water content). In the drier
soils (6-12% soil water content), leader length tended to decline as root volume
increased. This effect was most pronounced for the ddest treatment, in which
seedlings had the greatest reduction in growth at the highest root volume (Figure
3). At 115 days, however, the interaction was no longer significant. Terminal
growth of high root-volume category seedlings under low moisture conditions was
not significantly reduced. In fact, terminal length increased significantly with in-
creasing root volume (P = 0.01), regardless of soil water content (approximately
17% more growth from the smallest to the largest root-volume category) (Ta-
ble 4).
Unfortunately, terminal length was measured only at the time of harvest for
stored seedlings. As a result, data show only the positive influence of root volume
exhibited at the later stage of seedling establishment. As with unstored seedlings,
terminal length increased significantly (P = 0.0001) with increasing initial seedling
root volume (Table 4). An increase of 24% was found between the smallest and
the largest root-volume category.
284/FOREffrSCIENCE
lO
8
6
4
2
o
SOIL CONTENT I
ß 24%
I I I I
1 •2 3 4
ROOT-VOLUME CATEGORY
FIGURE 3. Terminal growth at 60 days of unstored seedlings by root volume category (standard error
= 0.56 cm).
When height growth was analyzed on a relative basis, root volume was found
to have little influence (Table 4). Seedlings with larger root volumes tended to
have slightly increased relative growth. In addition, initial seedling root volume
had little or no biologically significant effect on terminal needle length or density
on the terminal of both unstored and stored seedlings.
OTHER MORPHOLOGICAL CHARACTERISTICS
Stem diameter growth increased significantly with increasing soil water content
(Table 4). For unstored seedlings, stem diameter growth more than doubled
between the 6% and 24% soil water content treatments, and for stored seedlings,
stem diameter growth increased by more than 80%. Similarly, relative stem
diameter growth (mm diameter growth/mm initial stem diameter) was approxi-
mately doubled over the range of moisture treatments for both unstored and
stored seedlings.
MAY 1993/285
Initial root volume had little effect on stem diameter growth following trans-
planting. When analyzed on a relative basis, however, seedlings in the higher
root-volume categories exhibited significantly less relative stem diameter growth
than did seedlings in the smaller root-volume categories.
The number of buds produced on the seedling terminal increased significantly
with increasing root volume for both unstored and stored seedlings (P = 0.0001).
Increasing soil moisture content also produced a greater number of buds on
unstored seedlings. In addition, the root-volume/soil-moisture interaction on num-
ber of new terminal buds was significant in unstored seedlings. In all cases, the
number of buds increased with increasing soil water content. Number of buds also
increased with increasing root volume for treatments with soil water contents
between 12% and 24%, but varied within the 6% soil water content treatment.
The number of new laterals, from the preceding year's buds, was influenced
primarily by initial seedling root volume. For both unstored and stored seedlings,
the number of new laterals was nearly doubled between the smallest and the
largest root-volume category.
DRY MA'I•EER ALLOCATION
Dry weights of the seedling parts reflect the growth results. In every case,
seedlings grown in the driest soil had the lowest weights and those grown in the
most moist soil had the highest weights. Seedlings with the smallest initial root
volumes had the lowest weights and those with the largest root volumes had the
highest weights for all seedling components.
Total shoot-to-root ratio did not depend on initial root volume, but showed an
increasing trend with increasing soil water content in both unstored and stored
seedlings. Ratios of needle weights to their corresponding stem weights tended
to decrease with increasing root volume and increasing soil water content regard-
less of storage.
PHENOLOGY
The soil water content/root volume interaction was significant for number of days
to terminal and lateral budbreak for unstored seedlings. At relatively high water
contents (18-24%), the number of days to budbreak was generally constant,
regardless of root volume. However, at the lower water contents (6-12%), days
to budbreak tended to increase with increasing root volume. The effect was most
pronounced with the driest soil (6%): days to budbreak increased about 30%
between root volume category i (5-8 cm 3) and category 4 (14-20 cm 3) (Figure 4).
Number of days to terminal and lateral budbreak for stored seedlings did not
depend on either soil water content or initial seedling root volume.
DISCUSSION
Although significant in both cases, the effect of moisture stress was generally
more dramatic in seedlings transplanted immediately following lifting than it was
in seedlings transplanted following storage. Stored seedlings burst bud less than
286/FOREST•CIENCE
75
n- 70-
65-
z
J-- 60-
z
D
55-
0
m ,50-
z
45
SOIL WATER CONTENT .
ß 12• /
ß 18% /
I I I I
I 2 3 4
ROOT-VOLUME CATEGORY
FIGURE 4. Average number of days until terminal budbreak of unstored seedlings, by root-volume
category (standard error = 1.84 days).
3 wk after being transplanted, as would be expected for cold-stored seedlings
which have met their chilling requirements (van den Driessche 1977). As a result,
new growth began early in the treatment cycles when soil had not yet dried down.
Unstored seedlings, however, did not break bud until nearly 7 wk after trans-
planting, thus allowing for a longer period of treatment application before growth.
This explanation also holds for differences in the effect of soil water content on
number of days to budbreak in unstored and stored seedlings.
Stored seedlings showed less overall growth than did seedlings which were
transplanted immediately after lifting from the nursery. Studies have shown that
carbohydrate reserves of seedlings are depleted during storage (McCracken
1979, Ritchie 1982), reducing the amount of sugar available for new growth.
Furthermore, the stored seedlings were transplanted in early June and grown
during summer months when seedlings must expend more energy for respiration
under warmer temperatures (Kramer and Kozlowski 1979). Consequently,
MAY 1993/287
growth of stored seedlings was impeded by fewer resources and greater envi-
ronmental stress.
As we have stated, data for unstored and stored seedlings in these studies
cannot be compared statistically because of the differences in time, storage, and
growing environment. However, it is clear that the relative effects of soil water
content and root volume on transplant shock are similar for both, despite differ-
ences in magnitude. This repetition of results adds strength to the conclusion of
this study.
BOTTLE BRUSHING
Results of this study suggest that moisture stress is the primary factor causing
transplant shock. This can be explained physiologically. When a plant experiences
a water deficit, either from a lack of available soil water or from an inability of the
root system to uptake water following transplanting, there can be a loss of turgor
in the cells. As a result, cell size decreases, which leads to decreased leaf area,
reduced photosynthate production, and decreased growth (Chapin et al. 1987,
Hale and Orcutt 1987, DeYoe 1988). Furthermore, to compensate for loss of
turgor, a stressed seedling may allocate a portion of its solutes for osmotic
adjustment, further reducing availability of resources for growth (Morgan 1984,
Buxton et al. 1985).
This reduced growth limits water loss in the plant by decreasing the transpi-
rational area in new tissues. Blake (1983) found that needles in the new flush of
growth transpired 4-5 times the rate found in older needles of white spruce.
Moreover, transpiration rates of all needles can be reduced with decreasing soil
water potential (Babalola et al. 1968, Lopushinsky and Klock 1974) and the stress
of outplanting (Hallman et al. 1978). Studies have shown that newly planted trees
are prone to water stress even under conditions of high soil water potentials. For
example, Baldwin and Barney (1976) showed that planted lodgepole (Pinus con-
torta Dougl.) and ponderosa pine (Pinus ponderosa Laws.) seedlings have lower
water potentials, and thus experience greater water stress, than do established
trees for up to 2 yr after planting. Grossnickle (1988) reported daily turgor loss
in white spruce during the first 60 days after spring planting. Thus, until a seedling
is well established in its new environment, it can experience drought stress and
reduced growth. Burdett (1990) states that shoot growth in newly planted trees
is primarily dependent on successful root establishment. Once root growth has
resulted in attainment of a favorable plant water status, shoot growth can proceed
unchecked. However, low available soil moisture can hinder this process.
Moisture stress has been found to affect seedling development in many species.
Studies with red pine (Pinus resinosa Ait.) (Clements 1970, Garrett and Zahner
1973), Monterey pine (Kaufinann 1977), white spruce, and Engelmann spruce
(Picea engelmanni Parry) (Burdett et al. 1984) indicate that moisture stress often
causes shortened shoots and needles on seedlings. In addition, Hallgren and
Helms (1988) report that drought reduced the number of internodes and internode
elongation in California red fir (Abies magnifica A. Murr) and white fir (Abies
concolor [Gord. and Glend.] Lindl.). In a study with Ioblolly pine (Pinus taeda L.),
leaf area of seedlings subjected to repeated soil drying was significantly less than
that of well-watered control plants (Teskey et al. 1987). These findings are
consistent with the results of the current study.
288/FO•szscm•cE
Under well-irrigated treatments, root volume had little effect on early growth
of seedlings following transplanting. However, we hypothesized that the highest
root volume should have the greatest early growth in drier soils because of higher
root growth potential and greater absorption capacity (Carlson 1986, Carlson and
Miller 1990). The exact opposite was found to be the case.
This apparent inconsistency may be explained by the observation that seedlings
with higher root volumes had a greater number of branches. The number of new
lateral branches was significantly higher in seedlings with relatively large root
volumes. This increased number of new laterals may reflect a higher number of
buds present initially on many branches. Therefore, selecting for higher root
volume may also be selecting for higher leaf area and hence greater surface area
for transpiration. That the weight of old needles doubled from the smallest to the
largest root volume categories further supports this explanation. Livingston and
Black (1988) found that total dry matter of Douglas-fir was highly correlated with
leaf area (r 2 = 0.86), because photosynthesis is proportional to leaf area. Beineke
and Perry (1965) found a direct linear relationship between transpiration and size
of the root system in slash pine (Pinus elliottii Engelm.). Similarly, Carlson and
Miller (1990) found a positive correlation between root volume and leaf area in
1oblolly pine. However, in pines, root volume is also highly correlated with height,
which is related to leaf area. In this study with Douglas-fir, the relationship
between root volume and height was poor (r 2 -- 0.07). Nonetheless, because of
increased seedling branching, the relationship between root volume and leaf area
is probably significant.
In addition, pots with higher root volumes required more frequent watering,
which indicates relatively higher water uptake and demand. Thus, demand prob-
ably exceeds uptake by a greater margin in seedlings with the higher root volumes
during early growth in dry soils, and this results in reduced vigor. Day and
MacGillivray (1975) found that white spruce seedlings grown in low soil moisture
were unable to generate new roots despite a high capacity for root growth.
Similarly, Stone and Jenkinson (1970) found reduced root elongation of ponderosa
pine seedlings with decreasing available soil water. This could explain the in-
creased stress condition of seedlings with high transpiration rates (i.e., high root
volumes) in dry soils. Baker et al. (1979) found that seedlings with lower tran-
spirational area had higher survival and growth than those with higher transpira-
tional area on a droughty site. Because seedlings with high root volumes were
able to recover from their early disadvantage, this effect may be short-term,
present only for the first several weeks after transplanting, when the seedling's
root system reestablishes itself in the soil. After this period, seedlings with large
root volumes may outperform the others. Rose et al. (1991a, 1991b) found that
ponderosa pine and Douglas-fir seedlings with larger root volumes had signifi-
cantly higher growth and survival than did those with smaller root volumes after
two growing seasons on a harsh site.
OTHER MORPHOLOGICAL CHARACTERISTICS
Total stem diameter increased significantly with increasing root volume, and this
might have been expected given that initial stem diameter was highly correlated
with initial root volume (r 2 -- 0.72). Stem diameter growth, both absolute and
relative, decreased with increasing root volume, especially for seedlings with the
MAY 1993/289
highest initial root volumes grown in the ddest soil. This effect may be similar to
that noted for unstored seedlings during early growth and budbreak, in which
seedlings with relatively high root volumes had an early disadvantage, possibly
because of increased transpirational stress. In addition, a seedling with a large
stem diameter (and, hence, large root volume) must produce a greater volume of
new tissue than must one with a small stem diameter for the same increase in
diameter. For example, assuming a common height of 35 cm, a seedling which has
an initial stem diameter of 8 mm must produce approximately 1560 ram3 of new
tissue for a 1 mm increase in stem diameter, whereas a seedling with an initial
stem diameter of 4 mm need only produce approximately 825 ram3 of new tissue
for a 1 mm increase in diameter (D. Hann 1991, Dept. of For. Resour., Oregon
State Univ., pers. comm.).
Moisture stress was found to decrease bud production. This may affect the
subsequent year's growth as well. Environmental conditions during shoot devel-
opment can affect shoot growth the following year (Clements 1970, Garrett and
Zahner 1973, Pollard and Logan 1977). Livingston and Black (1988) found that
differences in leaf area between irrigation treatments became more pronounced in
successive growth seasons, suggesting that moisture stress affects not only the
current year's growth, but also the next year's growth. They attribute these
continued effects to a limited development of new leaf primordia under drought
conditions. Hallgren and Helms (1988) found that watering more than doubled the
number of primordia in red and white fir. These studies demonstrate the potential
long-term effects of transplant shock. However, when conditions are not limiting,
spruce (Macey and Arnott 1986) and Douglas-fir (Carlson et al. 1980) can com-
pensate for reduced predetermined foliage through free growth after replanting.
Seedlings with high root volumes tended to produce the most buds on the new
terminal, even in the driest treatment. High root volume seedlings also tended to
have a greater number of branches. Apparently, these seedlings are continuing to
produce a greater number of branches, even under conditions of water stress.
DRY MATTER ALLOCATION
Water stress has been found to alter the allocation of dry matter between root and
shoot. Teskey et al. (1987) found that when seedlings were exposed to repeated
drought cycles, dry matter allocation to the root increased significantly; this was
at the expense of allocation to the stem, but not the leaves. Similarly, Livingston
and Black (1988) found that Douglas-fir seedlings exposed to prolonged water
deficits had increased root development. Results of this study, however, indicate
that the dry weight of all plant parts, including the roots, decreased significantly
with increased moisture stress. Furthermore, regardless of soil water content or
initial root volume, the percentage of dry matter allocated to the roots remained
constant. A longer period of moisture stress in this study might have resulted in
increased root production similar to that found in other studies.
PHENOLOGY
Delayed budbreak with increasing water stress, found in an ongoing study with
the Nursery Technology Cooperative (unpublished data), as well as in a study by
Kaushal and Aussenac (1989), was expected in this study. Seedlings with large
290/FORF•SCIENCE
root volumes were expected to be most vigorous (i.e., initiate rapid budburst).
However, this was not the case, especially in the driest treatment. As with early
growth, seedlings with rehtively high root volumes, despite a high capacity for
water uptake, may actually be under greater transpirational stress. This stress
effectively reduces seedling vigor.
CONCLUSIONS AND RECOMMENDATIONS
These results indicate that the null hypotheses that moisture stress does not
cause transplant shock and that transplant shock is not a function of initial seedling
root volume are to be rejected. The primary cause of transplant shock in this
study appears to be moisture stress. In addition, seedlings with high root volumes
generally exhibit relatively fewer transplant shock symptoms. An exception to this
occurs under extreme drought conditions, when seedlings may have a disadvan-
tage prior to reestablishment of the root system. These relationships can be
applied to nursery grading standards in order to select the seedlings least likely to
go into shock following transplanting to a specific site. Choice of seedlings of
particular root volume sizes to be outplanted to sites of known moisture conditions
may improve growth and vigor of plantations. Results from a pot study of the
nature described, however, can be extrapolated only with caution to field condi-
tions.
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Copyright ¸ 1993 by the Society of American Foresters
Manuscript received January 14, 1992
AUTHORS AND ACKNOWLEDGMENTS
Diane L. Haase and Robin Rose are Faculty Research Assistant and Associate Professor, respec-
tively, Department of Forest Sdence, Oregon State University, Corvallis 97331. Research supported
by the Nursery Technology Cooperative. Valuable comments were provided by John Gleason, Dr.
Steve Hobbs, and Dr. Susan Stafford. We also thank Terri Houde, Gladwhn Joseph, Tom Popham, and
Bud Graham for their assistance with the study. Paper 2784 of the Forest Research Laboratory,
Oregon State University.
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Black spruce is the main tree species growing within peatlands. The difficult growing conditions within peatlands are associated to low individual wood productivity and only tree species tolerant to high ground water level can survive. We examine the effect of water-saturated soil on the growth potential of black spruce trees and specific adaptation of the root system. Experimental mesocosms were constructed with two drainage regimes (saturated and well-drained soil conditions). We measured biomass, height and diameter at stem base of 55 black spruce saplings and noted the location of each horizontal root. Black spruce exhibited a very shallow root system located above saturated commercial peat 19 years after the experiment was initiated. Most roots were adventitious in the water-saturated mesocosms. Overall aerial and root biomass accumulation of the black spruce trees growing under saturated soil conditions was significantly lower than that of the well-drained mesocosms. Interestingly, root-shoot ratios were similar across the two drainage regimes. Soil conditions induced adaptation of the root system in black spruce trees, and physiological stress affected the entire individual with lower biomass productivity in all components (stem, branches, root system). However, biomass distribution remained similar to that of trees growing in well-drained mesocosms.
... Many Douglas fir seedlings were lost shortly after planting, which significantly reduced the number of replicates for pure Douglas fir pots and pots where Douglas fir was mixed with European beech and Norway spruce. Douglas fir seedlings have been previously reported to be prone to transplanting shock [66]. Growing seedlings from seeds or cuttings can significantly increase the survival rates and yield seedlings that are better adapted to the experimental conditions than seedlings from a nursery [65]. ...
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Light availability is a crucial resource determining seedling survival, establishment, and growth. Competition for light is asymmetric, giving the taller individuals a competitive advantage for obtaining light resources. Species-specific traits, e.g., shade tolerance, rooting depth, and leaf morphology, determine their strategical growth response under limited resource availability and different competitive interactions. We established a controlled pot experiment using European beech, Norway spruce, and Douglas fir seedlings and applying three different light availability levels -10%, 20%, and 50%. The experiment's main aim was to better understand the effects of light availability and competition type on the growth, growth allocation, and biomass production of recently planted seedlings. We planted four seedlings per pot in either monocultures or mixtures of two species. Relative height and diameter growth and aboveground woody biomass of seedlings increased with increasing light availability. All seedlings allocated more growth to height than diameter with decreasing light availability. Seedlings that reached on average greater height in the previous year allocated less growth to height in the following year. Additionally, there were general differences in growth allocation to the height between gymnosperms and angiosperms, but we did not find an effect of the competitor's identity. Our mixture effect analysis trends suggested that mixtures of functionally dissimilar species are more likely to produce higher biomass than mixtures of more similar species such as the two studied conifers. This finding points towards increased productivity through complementarity.
... Manejo radicular El volumen radicular de las plantas de pino oregón es importante de considerar al momento de llevarlas al lugar del establecimiento, principalmente cuando existen condiciones de escasa humedad del suelo, que pueden provocar shock de transplante; en estos casos las plantas con un volumen radicular grande, generalmente presentan menos síntomas de shock que aquellas con pequeño volumen radicular (Haase y Rose, 1993). ...
... Field-transplanted nursery trees also present variable degrees of transplant stress, described as the disruption of physiological functions in seedlings. Transplant shock is mainly caused by low nutrient availability resulting from poor rootsoil contact, low water porosity of suberized roots, and mechanical root damage (Rietveld 1989;Haase and Rose 1993;Grossnickle 2005). Nurseries and reforestation programs can greatly benefit from AM biotization for the growth and establishment of seedlings used in forestry (Cordell et al. 1987;Perry et al. 1987;Pagano and Cabello 2011;Szabó et al. 2014). ...
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Walnut trees are among the most important hardwood species in the northern hemisphere, ecologically and economically. They are mainly cultivated for timber and nut production but are also attractive ornamental trees in parks. Establishing walnut orchards is difficult because seedlings have a coarse root architecture and few of them survive to transplanting. Planting success is mainly determined by the root system morphology and the nutrient status of the seedlings, so that rhizosphere conditions are critical for plant performance. Walnut trees can associate with soil-borne arbuscular mycorrhizal fungi, which are obligate biotrophs. In this association, plant-produced carbon compounds are traded against fungus-acquired soil mineral nutrients. The beneficial effect of arbuscular mycorrhizal symbiosis on hardwood seedling quality and field performance has long been known, but an integrated view is lacking about the effects of arbuscular mycorrhizas on walnut cropping. Therefore, we surveyed the literature published over the last 40 years to provide up-to-date knowledge on the relationships between arbuscular mycorrhizas and walnut trees. Our review outlines the major following points: (1) the arbuscular-mycorrhiza-mediated nutrient uptake capacity of walnut trees is associated with first- to third-order roots, and fibrous tip-ended roots are dependent on arbuscular mycorrhizal fungi, whereas pioneer roots are not; (2) early inoculation with arbuscular mycorrhizal fungi improves the survival and seedling performance attributes of transplanted walnut trees: biotization enhances walnut transplant success by increasing the number of lateral roots and plant P uptake, but these benefits are fungus- and host-dependent; (3) in the context of walnut agroforestry, deeply rooted walnut trees play a role as reservoirs of arbuscular mycorrhizal fungal propagules for the surrounding vegetation, but tree shade and soluble phosphate availability decrease walnut mycorrhizal dependency; and (4) the arbuscular mycorrhizal mycelium mediates the transport of juglone and thus plays a role in walnut tree allelopathy.
Thesis
Le noyer anglais (Juglans regia L.) est la principale espèce cultivée pour la production de noix comestibles. Sa canopée peu dense et son système d'enracinement profond font du noyer une espèce idéale pour la culture en allées, une pratique agroforestière pouvant améliorer la productivité en favorisant les mécanismes de facilitation inter-plantes. L'agroforesterie du noyer fruitier nécessite la production à grande échelle de porte-greffes (PG) sélectionnés pour offrir le meilleur ancrage, la meilleure vigueur et la meilleure tolérance aux agents pathogènes. En raison de l'hétérozygotie du noyer qui ne reproduit pas à l'identique ces caractéristiques, la multiplication végétative in vitro joue un rôle clé dans la propagation des PG de noyer fruitier de qualité. La micropropagation des explants végétaux nécessite une phase d'acclimatation ex vitro pour réparer les anomalies induites in vitro, puis une post-acclimatation en serre lorsque les plantules deviennent photoautotrophes. Cependant, une faible survie et des taux de croissance lents sont des difficultés courantes rencontrées dans les pépinières lors de l'établissement de vitroplants. Comme beaucoup d'arbres fruitiers et à noix, le noyer présente une forte dépendance à l'égard des champignons mycorhiziens à arbuscules (MA) symbiotiques du sol pour sa nutrition phosphatée et son développement en raison de racines peu ramifiées qui limitent l'absorption du phosphate inorganique du sol (Pi). Dans le contexte de la production de PG de noyer fruitier, cette thèse a consisté à analyser, à différents stades de développement, l'établissement de sept PG présentant un intérêt économique, après inoculation ou non par un champignon MA dans des conditions contrastées de disponibilité en Pi. Nous avons démontré que la biotisation par le champignon MA Rhizophagus irregularis améliore le développement des PG lors de l'acclimatation ex vitro et post-vitro. Lors d'une carence en Pi, la biotisation augmente comparativement aux témoins les caractéristiques de performance des vitroplants, notamment la biomasse, le nombre de feuilles, la hauteur des tiges, l'efficacité photosynthétique et la nutrition foliaire (carbone, azote, Pi). Toutefois, ces avantages dépendent du PG, suggérant un recrutement différentiel de la voie d'absorption symbiotique du Pi selon le cultivar étudié. Ceci nous a conduit à identifier chez les Juglans spp. les transporteurs de Pi inductibles par la mycorhization. La détection des orthologues putatifs du transporteur de phosphate MtPT4 spécifique de la symbiose MA chez la légumineuse modèle Medicago truncatula, réalisée avec Orthofinder à l'aide de l'algorithme BLAST all-vs-all, a permis d'identifier trois orthologues putatifs chez J. regia et chez J. microcarpa. Nous avons validé ces candidats par l'étude comparative de leur expression après inoculation ou non par R. irregularis dans des conditions contrastées de disponibilité en Pi. Afin d'étudier les avantages de la mycorhization du noyer en culture en allées, nous avons simulé à l'aide de microcosmes compartimentés un système agroforestier dans lequel le PG RX1 (J. regia x J. microcarpa) est relié ou non par un réseau mycélien commun (RMC) à des racines de maïs (Zea maize L.), cultivé dans des conditions contrastées de disponibilité en Pi. En huit semaines, le réservoir de propagules fongiques formé par les racines de noyer a permis la mycorhization du maïs, autorisant ainsi un accès aux résidus de fertilisation. Nous avons montré que le RMC développé lors d'une carence en Pi conduit chez les deux plantes en co-culture à des bénéfices en termes de croissance et de nutrition, comparables à ceux observés sans mycorhization et sans carence. Cette étude démontre qu'un RMC peut pallier une carence phosphatée chez le maïs et le noyer élevés en co-culture, et donc contribuer à limiter l'apport d'intrants chimiques en systèmes agroforestiers.
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Demand for nursery stock of Japanese larch (Larix kaempferi) is growing. Containerized seedlings are expected to meet this demand. However, the conventional methods are labor intensive and time consuming because one-year-old bare-root seedlings are transplanted to containers. In this study, we selected seeds using a spectroscope and examined two propagation methods, direct sowing on nursery container (direct sowing) and sowing on a small plug tray followed by transplantation to a container (plug transplant), to shorten the nursery period of 2 years. Germination rate increased in the selected seed when compared with the unselected seed (χ² test). The days to germinate (DtG) shortened with the use of heavier seeds, and the one-year-old seedlings grew taller as the DtG decreased. However, transplantation from plug trays had negative effects (generalized linear model (GLM) and analysis of variance (ANOVA). On the other hand, large volume cell had positive effects on root collar diameter (GLM and ANOVA). The results revealed that the nursery periods were shortened by using large volume cell, irrespective of the seedling type (direct sowing or plug transplant).
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Survival and development of outplanted 2-0 and 2-1 white spruce nursery stock, transplanted 3-0 and 4-0 wildlings and 3-0 and 4-0 undisturbed wildlings are compared. Mortality was negligible in all groups. Planting check caused a 47% reduction in height increment during the first year and 15% during the second year after planting. The height increment was best related to the height growth during the previous year and total height of the planting stock. Insignificant differences were found between plants on undisturbed soil surface and those on exposed mineral soil.
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Several age-classes of nursery stock were sampled before and after the 1963 growing season by excavation of trees. Samples were also planted out and later excavated. Studies of several criteria to express check were made and leader length selected as the most practicable.It is suggested that, by definition, a tree be considered in check until it has achieved a rate of terminal growth equivalent to that it would have attained in the next season in the nursery. Average leader lengths of unchecked trees are suggested for 2-0, 3-0 and 2-2 stock. Check was found to reduce leader length by about 50% in the first year after outplanting. Other experiments indicate that the effect continued for ten years or more in many instances.
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Plantation performance depends on the outcome of an interaction between the stock planted and its environment. Immediately after planting, it is the degree to which stock is pre-adapted to site conditions (i.e., its phenotype), rather than its genetic potential for adaptation to environment (i.e., its genotype) which has the greatest influence on performance. The purpose of a stock quality control system is to ensure that stock has phenotypic characteristics which adapt it to the planting site. Thus a prerequisite to the creation of an effective quality control system is the definition of stock quality standards which specify the phenotypic characteristics of stock adapted to the conditions of normal use. Physiological principles provide a basis for such standards but they must be refined through trial and error. Thus feedback on the performance of stock conforming to current standards is one key to the development of appropriate stock quality standards. Another is research to determine the causes of unsatisfactory performance. With these sources of information it is possible to modify stock standards or site treatments in a way that improves the cost-effectiveness of regeneration efforts. Culling, the traditional method of quality control, can reduce stock heterogenity, but it cannot transform poor stock into good. Often, therefore, the attainment of a desired quality standard requires an overall improvement in the quality of nursery output. The only practical way of doing this is to modify the nursery environment including cultural and handling practices.
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Observations were made on growth of white spruce Picea glauca and Engelmann spruce P. engelmannii, each planted at a single location in the interior of British Columbia. Results are consistent with the hypothesis that, as root establishment proceeds, shoot growth tends to be limited by the supply first of water, then of mineral nutrients. This implies that the early growth of planted spruce can be maximized by using stock with a high root growth capacity, or other adaptations to drought, and applying slow release fertilizer at planting.-from Authors