Ling-Hao Li’s research while affiliated with Chinese Academy of Sciences and other places

Predicted future shifts in the magnitude and frequency (larger but fewer) of precipitation events and enhanced nitrogen (N) deposition may interact to affect grassland productivity, but the effects of N enrichment on the productivity response to individual precipitation events remain unclear. In this study, we quantified the effects of N addition on the response patterns of gross primary productivity (GPP) to individual precipitation events of different sizes (Psize) in a temperate grassland in China. The results showed that N enrichment significantly increased the time-integrated amount of GPP in response to an individual precipitation event (GPPtotal), and the N-induced stimulation of GPP increased with increasing Psize. N enrichment rarely affected the duration of the GPP response, but it significantly stimulated the maximum absolute GPP response. Higher foliar N content might play an important role in the N-induced stimulation of GPP. GPPtotal in both the N-addition and control treatments increased linearly with Psize with similar Psize intercepts (approximately 5 mm, indicating a similar lower Psize threshold to stimulate the GPP response) but had a steeper slope under N addition. Our work indicates that the projected larger precipitation events will stimulate grassland productivity, and this stimulation might be amplified by increasing N deposition.

Upland forests are traditionally thought to be net sinks for atmospheric methane ( CH 4 ). In such forests, in situ CH 4 fluxes on tree trunks have been neglected relative to soil and canopy fluxes. We measured in situ CH 4 fluxes from the trunks of living trees and other surfaces, such as twigs and soils, using a static closed‐chamber method, and estimated the CH 4 budget in a temperate upland forest in Beijing. We found that the trunks of Populus davidiana emitted large quantities of CH 4 during July 2014–July 2015, amounting to mean annual emissions of 85.3 and 103.1 μg m ⁻² h ⁻¹ on a trunk surface area basis on two replicate plots. The emission rates were similar in magnitude to those from tree trunks in wetland forests. The emitted CH 4 was derived from the heartwood of trunks. On a plot or ecosystem scale, trunk CH 4 emissions were equivalent to c . 30–90% of the amount of CH 4 consumed by soils throughout the year, with an annual average of 63%. Our findings suggest that wet heartwoods, regardless of rot or not, occur widely in living trees on various habitats, where CH 4 can be produced.

Based on the long-term cutting experiment, this paper analyzed the responses of the aboveground biomass of five dominant and subdominant plant species and the community stability in a Stipa krylovii steppe of Inner Mongolia to various cutting height. Cutting with a stubble height of > 10 cm had slight effects on the aboveground biomass of the five species. Cutting with a stubble height of 10 cm benefited the growth of Artemisia frigida but made against the growth of Stipa krylovii. Cleistogenes squarrosa at the stubble height of 2 cm performed best, and Carex korshinskyi at the stubble height of 5 cm contributed most to the community, with the biomass positively correlated with the cutting years. Potentilla acaulis growth was detrimentally affected at the stubble heights of 2 and 15 cm. Overall, perennial species with higher plant height and stronger competitive ability were more tolerant to disturbances, and a minimum cutting height of 10 cm should be applied to maintain a high stability of the steppe ecosystem.

The industrially important organism Corynebacterium glutamicum has been characterized in recent years for its robust ability to assimilate aromatic compounds. In this study, C. glutamicum strain AS 1.542 was investigated for its ability to catabolize phenylacetic acid (PAA). The paa genes were identified; they are organized as a continuous paa gene cluster. The type strain of C. glutamicum, ATCC 13032, is not able to catabolize PAA, but the recombinant strain ATCC 13032/pEC-K18mob2::paa gained the ability to grow on PAA. The paaR gene, encoding a TetR family transcription regulator, was studied in detail. Disruption of paaR in strain AS 1.542 resulted in transcriptional increases of all paa genes. Transcription start sites and putative promoter regions were determined. An imperfect palindromic motif (5′-ACTNACCGNNCGNNCGGTNAGT-3′; 22 bp) was identified in the upstream regions of paa genes. Electrophoretic mobility shift assays (EMSA) demonstrated specific binding of PaaR to this motif, and phenylacetyl coenzyme A (PA-CoA) blocked binding. It was concluded that PaaR is the negative regulator of PAA degradation and that PA-CoA is the PaaR effector. In addition, GlxR binding sites were found, and binding to GlxR was confirmed. Therefore, PAA catabolism in C. glutamicum is regulated by the pathway-specific repressor PaaR, and also likely by the global transcription regulator GlxR. By comparative genomic analysis, we reconstructed orthologous PaaR regulons in 57 species, including species of Actinobacteria, Proteobacteria, and Flavobacteria, that carry PAA utilization genes and operate by conserved binding motifs, suggesting that PaaR-like regulation might commonly exist in these bacteria.

Purpose Global nitrogen deposition has profound impact on the terrestrial ecosystem including the semiarid temperate grassland, causing vegetation community shifts and soil acidification. Little is known regarding the effect of nitrogen (N) deposition on the belowground microbial communities. This study aimed to examine the response of ammonia-oxidizing bacteria (AOB) and archaea (AOA) to added N in semiarid temperate grassland. Materials and methods We studied the changes of AOB and AOA by using molecular techniques targeting amoA genes along a urea fertilization gradient, i.e., 0, 1, 2, 4, 8, 16, 32, 64 g N m−2 year−1, in a 6-year field experiment of semiarid temperate grassland, Inner Mongolia of China. Results and discussion AOB community responded to urea–N substrate clearly, and N addition rates 2–4 g N m−2 year−1 induced an increase in its abundances and the shift of its composition. However, AOA community remained unchanged and the highest N loading at 64 g N m−2 year−1 even decreased its abundance. Moreover, higher N loading rates (more than 16 g N m−2 year−1) significantly decreased the diversity of AOB but not AOA, as indicated by the decrease of its Shannon and Evenness indices. Conclusions The relative long-term nitrogen loading of more than 2–4 g N m−2 year−1 resulted in diversity loss of AOB in this semiarid temperate grassland. Increasing N loading altered AOB abundance and composition, but AOA showed nonsignificant changes.

Methane (CH(4)) may be generated via microbial and nonmicrobial mechanisms. Nonmicrobial CH(4) is also ubiquitous in nature, such as in biomass burning, the Earth's crust, plants, and animals. Relative to microbial CH(4), nonmicrobial CH(4) is less understood. Using fresh (living) and dried (dead) leaves and commercial structural compounds (dead) of plants, a series of laboratory experiments have been conducted to investigate CH(4) emissions under aerobic and anaerobic conditions. CH(4) emissions from fresh leaves incubated at ambient temperatures were nonmicrobial and enhanced by anaerobic conditions. CH(4) emissions from dried leaves incubated at rising temperature ruled out a microbial-mediated formation pathway and were plant-species-dependent with three categories of response to oxygen levels: enhanced by aerobic conditions, similar under aerobic and anaerobic conditions, and enhanced by anaerobic conditions. CH(4) emissions in plant structural compounds may help to fully understand nonmicrobial CH(4) formation in plant leaves. Experiments of reactive oxygen species (ROS) generator and scavengers indicate that ROS had a significant role in nonmicrobial CH(4) formation in plant material under aerobic and anaerobic conditions. However, the detailed mechanisms of the ROS were uncertain.