[Show abstract][Hide abstract] ABSTRACT: Specific leaf area (SLA), a key element of the 'worldwide leaf economics spectrum', is the preferred 'soft' plant trait for assessing soil fertility. SLA is a function of leaf dry matter content (LDMC) and leaf thickness (LT). The first, LDMC, defines leaf construction costs and can be used instead of SLA. However, LT identifies shade at its lowest extreme and succulence at its highest, and is not related to soil fertility. Why then is SLA more frequently used as a predictor of soil fertility than LDMC?
SLA, LDMC and LT were measured and leaf density (LD) estimated for almost 2000 species, and the capacity of LD to predict LDMC was examined, as was the relative contribution of LDMC and LT to the expression of SLA. Subsequently, the relationships between SLA, LDMC and LT with respect to soil fertility and shade were described.
Although LD is strongly related to LDMC, and LDMC and LT each contribute equally to the expression of SLA, the exact relationships differ between ecological groupings. LDMC predicts leaf nitrogen content and soil fertility but, because LT primarily varies with light intensity, SLA increases in response to both increased shade and increased fertility.
Gradients of soil fertility are frequently also gradients of biomass accumulation with reduced irradiance lower in the canopy. Therefore, SLA, which includes both fertility and shade components, may often discriminate better between communities or treatments than LDMC. However, LDMC should always be the preferred trait for assessing gradients of soil fertility uncoupled from shade. Nevertheless, because leaves multitask, individual leaf traits do not necessarily exhibit exact functional equivalence between species. In consequence, rather than using a single stand-alone predictor, multivariate analyses using several leaf traits is recommended.
Annals of Botany 09/2011; 108(7):1337-45. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Genome size is a function, and the product, of cell volume. As such it is contingent on ecological circumstance. The nature of 'this ecological circumstance' is, however, hotly debated. Here, we investigate for angiosperms whether stomatal size may be this 'missing link': the primary determinant of genome size. Stomata are crucial for photosynthesis and their size affects functional efficiency.
Stomatal and leaf characteristics were measured for 1442 species from Argentina, Iran, Spain and the UK and, using PCA, some emergent ecological and taxonomic patterns identified. Subsequently, an assessment of the relationship between genome-size values obtained from the Plant DNA C-values database and measurements of stomatal size was carried out.
Stomatal size is an ecologically important attribute. It varies with life-history (woody species < herbaceous species < vernal geophytes) and contributes to ecologically and physiologically important axes of leaf specialization. Moreover, it is positively correlated with genome size across a wide range of major taxa.
Stomatal size predicts genome size within angiosperms. Correlation is not, however, proof of causality and here our interpretation is hampered by unexpected deficiencies in the scientific literature. Firstly, there are discrepancies between our own observations and established ideas about the ecological significance of stomatal size; very large stomata, theoretically facilitating photosynthesis in deep shade, were, in this study (and in other studies), primarily associated with vernal geophytes of unshaded habitats. Secondly, the lower size limit at which stomata can function efficiently, and the ecological circumstances under which these minute stomata might occur, have not been satisfactorally resolved. Thus, our hypothesis, that the optimization of stomatal size for functional efficiency is a major ecological determinant of genome size, remains unproven.
Annals of Botany 04/2010; 105(4):573-84. · 3.45 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A simple protocol is presented for a functional classification of European grassland species using attributes that can be quickly and easily measured. These attributes relate to habitat fertility, intensity of grazing and disturbance. As a surrogate for habitat fertility we use leaf nitrogen predicted by multiple regression from three leaf characters, specific leaf area, dry matter content and size. Average maximum canopy height of the component species of our vegetation, weighted by abundance, provides a rough assessment of the intensity of grazing. The percentage of annuals and vernal geophytes assesses disturbance. Functional descriptions of the CLIMB grasslands were produced and trends relating to both ecosystem and economic processes were detected. Most importantly, our estimate of habitat fertility predicts land use change. Within NW Europe the threat to grassland of conservation value from agricultural ‘improvement’ increases with fertility while in the Mediterranean increased fertility decreases the likelihood of abandonment. These mathematical relationships between an ecological attribute and a perception of economic potential can help us to routinely combine ecological and economic data. This is an important preliminary step as we attempt to reconcile practical economic concerns and conservation objectives within working landscapes.
Basic and Applied Ecology 01/2005; 6(2):119–131. · 2.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Conservation initiatives are failing to arrest the global loss of biodiversity. From our mechanistic studies of ecology and economics, we suggest that for grazing lands the root cause of this failure is a powerful economic deterrent to measures designed to protect diversity. We identify an exponential relationship between monetary returns and intensification of farming methods over an extremely wide range of grassland productivities and farm systems. At intermediate to high levels of fertility, however, this exponential increase in financial benefit from intensification is associated with a decline in biodiversity and an acceleration of the ecological processes driving species losses from grassland ecosystems.