Phosphorus (P) is one of the most limiting macronutrients for crop productivity and P deficiency is a common phenomenon in agricultural soils worldwide. Despite long-term application of phosphate fertilizers to increase crop yields, P availability is often low, due to the high affinity of phosphate for the soil solid phase. It has been suggested that the accumulated (surplus) P in agricultural soils is sufficient to sustain crop yields worldwide for about 100years. In this paper, we try to clear up the potential for making use of legacy P in soils for crop growth potentially alleviating the global P resource shortage. Specifically, we try to clear up the potential of soil "P activators" for releasing fixed P. P activators accelerate and strengthen process which transform P into bio-available forms via a range of chemical reactions and biological interactions. They include phosphate solubilizing microorganisms, phosphatase enzymes and enzyme activators, low molecular weight organic acids, humic acids, lignin, crop residues, biochar and zeolites. Although reported performance is variable, there is growing evidence that P activators can promote the release of phosphate from soil and, hence, have potential for mitigating the impending global P crisis. Further basic and applied research is required to better understand the mechanisms of interaction of P activators with natural soils and to maximize activator efficacy.

Abstract. Subtropical forests in southern China have received chronically large amounts of atmogenic nitrogen (N), causing N saturation. Recent studies suggest that a significant proportion of the N input is returned to the atmosphere, in part as nitrous oxide (N2O). We measured N2O emission fluxes by closed chamber technique throughout two years in a Masson pine-dominated headwater catchment with acrisols (pH ~ 4) at Tieshanping (Chongqing, SW China) and assessed the spatial and temporal variability in two landscape elements typical for this region: a mesic forested hillslope (HS) and a hydrologically connected, terraced groundwater discharge zone (GDZ) in the valley bottom. High emission rates of up to 1800 μg N2O-N m−2 h−1 were recorded on the HS shortly after rain storms during monsoonal summer, whereas emission fluxes during the dry winter season were generally low. Overall, N2O emission was lower in GDZ than on HS, rendering the mesic HS the dominant source of N2O in this landscape. Temporal variability of N2O emissions on HS was largely explained by soil temperature (ST) and moisture, pointing at denitrification as a major process for N removal and N2O production. The concentration of nitrate (NO3−) in pore water on HS was high even in the rainy season, apparently never limiting denitrification and N2O production. The concentration of NO3− decreased along the terraced GDZ, indicating efficient N removal, but with moderate N2O-N loss. The extrapolated annual N2O fluxes from soils on HS (0.54 and 0.43 g N2O-N m−2 yr−1 for a year with a wet and a dry summer, respectively) are among the highest N2O fluxes reported from subtropical forests so far. Annual N2O-N emissions amounted to 8–10% of the annual atmogenic N deposition, suggesting that forests on acid soils in southern China are an important, hitherto overlooked component of the anthropogenic N2O budget.

Cucumber gray mold caused by Botrytis cinerea is considered one of the most serious cucumber diseases. With the advent of Hi-seq technology, it is possible to study the plant–pathogen interaction at the transcriptome level. To the best of our knowledge, this is the first application of RNA-seq to identify cucumber and B. cinerea differentially expressed genes (DEGs) before and after the plant–pathogen interaction. In total, 248,908,688 raw reads were generated; after removing low-quality reads and those containing adapter and poly-N, 238,341,648 clean reads remained to map the reference genome. There were 3,512 cucumber DEGs and 1,735 B. cinerea DEGs. GO enrichment and KEGG enrichment analysis were performed on these DEGs to study the interaction between cucumber and B. cinerea. To verify the reliability and accuracy of our transcriptome data, 5 cucumber DEGs and 5 B. cinerea DEGs were chosen for RT-PCR verification. This is the first systematic transcriptome analysis of components related to the B. cinerea–cucumber interaction. Functional genes and putative pathways identified herein will increase our understanding of the mechanism of the pathogen–host interaction.

) were applied as a single dose to replicated plots at two positions along the hill slope (at top and bottom, respectively) during monsoonal summer. During a 6-day period after label application, we found that 71-100 % of the emitted N 2 O was derived from the labeled NO 3 -pool irrespective of slope position. Based on this, we assume that denitrification is the dominant process of N 2 O formation in these forest soils. Within 6 days after label addition, the fraction of the added 15 N-NO 3 -emitted as 15 N-N 2 O was highest at the low-N addition plots (0.2 g N m -2) , amounting to 1.3 % at the top position of the hill slope and to 3.2 % at the bottom position, respectively. Our data illustrate the large potential of acid forest soils in subtropical China to form N 2 O from excess NO 3 -most likely through denitrification.

In forests of the humid subtropics of China, chronically elevated nitrogen (N) deposition, predominantly as ammonium (NH ), causes significant nitrate (NO ) leaching from well-drained acid forest soils on hill slopes (HS), whereas significant retention of NO occurs in near-stream environments (groundwater discharge zones, GDZ). To aid our understanding of N transformations on the catchment level, we studied spatial and temporal variabilities of concentration and natural abundance (δ N and δ O) of nitrate (NO ) in soil pore water along a hydrological continuum in the N-saturated Tieshanping (TSP) catchment, southwest China. Our data show that effective removal of atmogenic NH and production of NO in soils on HS were associated with a significant decrease in δ N-NO , suggesting efficient nitrification despite low soil pH. The concentration of NO declined sharply along the hydrological flow path in the GDZ. This decline was associated with a significant increase in both δ N and δ O of residual NO , providing evidence that the GDZ acts as an N sink due to denitrification. The observed apparent N enrichment factor (ε) of NO of about -5‰ in the GDZ is similar to values previously reported for efficient denitrification in riparian and groundwater systems. Episode studies in the summers of 2009, 2010 and 2013 revealed that the spatial pattern of δ N and δ O-NO in soil water was remarkably similar from year to year. The importance of denitrification as a major N sink was also seen at the catchment scale, as largest δ N-NO values in stream water were observed at lowest discharge, confirming the importance of the relatively small GDZ for N removal under base flow conditions. This study, explicitly recognizing hydrologically connected landscape elements, reveals an overlooked but robust N sink in N-saturated, subtropical forests with important implications for regional N budgets.

Genes have been thought to affect community ecology and evolution, but their identification at the whole-genome level is challenging. Here, we develop a conceptual framework for the genome-wide mapping of quantitative trait loci (QTLs) that govern interspecific competition and cooperation. This framework integrates the community ecology theory into systems mapping, a statistical model for mapping complex traits as a dynamic system. It can characterize not only how QTLs of one species affect its own phenotype directly, but also how QTLs from this species affect the phenotype of its interacting species indirectly and how QTLs from different species interact epistatically to shape community behavior. We validated the utility of the new mapping framework experimentally by culturing and comparing two bacterial species, Escherichia coli and Staphylococcus aureus, in socialized and socially isolated environments, identifying several QTLs from each species that may act as key drivers of microbial community structure and function.

Responses of transpiration (Ec) to rain pulses are presented for two semiarid tree species in a stand of Pinus tabulaeformis and Robinia pseudoacacia. Our objectives are to investigate (1) the environmental control over the stand transpiration after rainfall by analyzing the effect of vapor pressure deficit (VPD), soil water condition, and rainfall on the post-rainfall Ec development and recovery rate, and (2) the species responses to rain pulses and implications on vegetation coverage under a changing rainfall regime. Results showed that the sensitivity of canopy conductance (Gc) to VPD varied under different incident radiation and soil water conditions, and the two species exhibited the same hydraulic control (-dG c/dlnVPD to Gcref ratio) over transpiration. Strengthened physiological control and low sapwood area of the stand contributed to low Ec. VPD after rainfall significantly influenced the magnitude and time series of post-rainfall stand Ec. The fluctuation of post-rainfall VPD in comparison with the pre-rainfall influenced the Ec recovery. Further, the stand Ec was significantly related to monthly rainfall, but the recovery was independent of the rainfall event size. Ec enhanced with cumulative soil moisture change (ΔVWC) within each dry-wet cycle, yet still was limited in large rainfall months. The two species had different response patterns of post-rainfall Ec recovery. Ec recovery of P. tabulaeformis was influenced by the pre- and post-rainfall VPD differences and the duration of rainless interval. R. pseudoacacia showed a larger immediate post-rainfall Ec increase than P. tabulaeformis did. We, therefore, concluded that concentrated rainfall events do not trigger significant increase of transpiration unless large events penetrate the deep soil and the species differences of Ec in response to pulses of rain may shape the composition of semiarid woodlands under future rainfall regimes.

Chronically elevated deposition of reactive nitrogen (N), as ammonium (NH 4 +) and nitrate (NO 3 À), in subtropical forests with monsoonal climate has caused widespread N leaching in southern China. So far, little is known about the effect of further increases in N input and changes in the relative proportion of NH 4 + and NO 3 À on turnover rate and fate of atmogenic N. Here we report a 15 N tracer experiment in Tieshanping (TSP) forest, SW China, conducted as part of a long-term N fertilization experiment, using NH 4 NO 3 and NaNO 3 , where effects of a doubling of monthly N inputs were compared. In June 2012, the regular N fertilizers were replaced by their 15 N-labeled forms, viz., 15 NH 4 NO 3 and Na 15 NO 3 , as a single-dose addition. Mass balances of N for the initial 1.5 years following label addition showed that for both treatments, 70% to 80% of the annual N input was leached as NO 3 À , both at ambient and at double N input rates. This confirms the earlier reported extreme case of N saturation at TSP. The 15 N, added as Na 15 NO 3 , showed recoveries of about 74% in soil leachates, indicating that NO 3 À input at TSP is subject to a rapid and nearly quantitative loss through direct leaching as a mobile anion. By contrast, recoveries of 15 N in soil leachates of only 33% were found if added as 15 NH 4 NO 3. Much of the 15 N was immobilized in the soil and to a lesser extent in the vegetation. Thus, immobilization of fresh N input is significantly greater if added as NH 4 + , than as NO 3 À .