Abstract Atmospheric acidic deposition has been a major environmental problem since the industrial revolution. However, our understanding of the effect of acidic deposition on soil pH is inconclusive. Here we examined temporal variations in topsoil pH and their relationships with atmospheric sulfur and nitrogen deposition across China's forests from the 1980s to the 2000s. To accomplish this goal, we conducted artificial neural network simulations using historical soil inventory data from the 1980s and a data set synthesized from literature published after 2000. Our results indicated that significant decreases in soil pH occurred in broadleaved forests, while minor changes were observed in coniferous and mixed coniferous and broadleaved forests. The magnitude of soil pH change was negatively correlated with atmospheric sulfur and nitrogen deposition. This relationship highlights the need for stringent measures that reduce sulfur and nitrogen emissions so as to maintain ecosystem structure and function.
Abstract Plant density and nitrogen (N) availability influence plant survival and nutrient use strategies, but the interaction between these two factors for plant growth and the balance of elements remains poorly addressed. Here, we conducted experimental manipulations using Arabidopsis thaliana, with the combination of four levels of plant density and four levels of N addition, and then examined the corresponding changes in plant biomass production (indicated by total plant biomass and biomass partitioning) and nutrient use strategies (indicated by leaf N and phosphorus (P) stoichiometry). The biomass–density relationship was regulated by N availability, with a negative pattern in low N availability but an asymptotic constant final yield pattern at high N availability. Excessive N addition reduced plant growth at low plant density, but this effect was alleviated by increasing plant density. The root to shoot biomass ratio increased with plant density at low N availability, but decreased at high N availability. N availability was more important than plant density in regulating leaf N and P stoichiometry, with the increasing leaf N concentration and decreasing leaf P concentration under increasing N addition, resulting in a negative scaling relationship between these two elemental concentrations. Our results show that N availability and plant density interactively regulate plant biomass production and leaf stoichiometry of A. thaliana, and highlight that the interactive effects of these two factors should be considered when predicting plant growth behaviour under intraspecific competitive environments in the context of nutrient changes.
ABSTRACT Aim To investigate broad‐scale patterns of plant leaf ash content and their possible causes in China. Location Mainland China and Hainan island, with the geographic ranges for the data used from 18.7° N to 49.2° N and 76.0° E to 128.3° E. Methods By analysing a data set of 2022 leaf samples, involving 704 species of terrestrial plants. Results Leaf ash content increases with increasing latitude at an average rate of 2.7 mg ash g −1 dry weight per degree latitude from south to north of China. Plant functional group shows a more powerful influence on the spatial variation in leaf ash than soil pH and climate. Fast‐growing species or those with leaves with a short life span have higher leaf ash than slow‐growing species or those with a long leaf life span. Plants from alkaline soils have higher leaf ash than those from acid soils (39.5 mg g −1 increase in leaf ash content per unit increase of pH). Increasing precipitation significantly reduces leaf ash (with a mean rate of 4.8 mg g −1 for every 100 mm rainfall), whereas the effect of temperature appears to be nonlinear. Main conclusions This study shows a significant latitudinal trend in leaf ash content in China. This geographic pattern is possibly shaped by the floral, edaphic and climatic factors that control the biogeochemical cycling of plant minerals. The results suggest that leaf ash content is a useful biogeographic indicator that can be used to explore the complex interactions between plants and the environment.
Common reed (Phragmites australis (Cav.) Trin. ex Steud.) is distributed widely throughout the world with various ecotypes. This research compares the functional traits and biomass allocation patterns of two contrasting reed ecotypes. Twelve pairs of aquatic and terrestrial reed samples were collected in northern China. Significant differences in functional traits between the two reed ecotypes were observed, while biomass allocation patterns of reed organs did not differ significantly except for at the root. The dry matter content (DMC) in the whole of the reed plant, leaf, root, and rhizome was higher; while the specific leaf area (SLA) and specific root length (SRL) were lower in terrestrial versus aquatic reed. The biomass allocation in organs of the two forms of reed was isometric, only root in the terrestrial habitat increased faster with an increase in the whole plant biomass. It can be affirmed that aquatic and terrestrial reed that adapt to different environments generally has distinct leaf and root functional traits but isometric biomass allocation patterns. This suggests different resource acquisition strategies: (1) aquatic reed grows faster with high SLA and SRL and is more responsive to the environment, while (2) terrestrial reed with high DMC grows slower and is less responsive to the adverse environment (e.g. dry soil conditions).
Abstract. Previous work has failed to address fully the response of (autotrophic and heterotrophic) respiration to grazing in different ecosystems, particularly in alpine grasslands outside the growing season. From 2010 to 2011 a field experiment combined two methods (static closed chambers and a closed dynamic soil CO2 flux system) in alpine grasslands located in the Tianshan Mountains. We examined the effects of grazing regime on ecosystem respiration (Re) both outside (NGS) and during (GS) the growing season and determined the pattern of Re in relation to climate change. There was no significant change in CO2 emissions under grazing. Heterotrophic respiration (Rh) accounted for 78.5% of Re with short-term grazing exclusion and 93.2% of Re with long-term grazing exclusion. Re, Rh and autotrophic respiration (Ra) fluxes outside the growing season were equivalent to 12.9%, 14.1% and 11.4% of the respective CO2 fluxes during the growing season. In addition, our results indicate that soil water content played a critical role in Ra in the cold and arid environment. Both Rh and Re were sensitive to soil temperature. Moreover, our results suggest that grazing exerted no significant effect on CO2 emissions in these alpine grasslands.
Combined effects of cumulative nutrient inputs and biogeochemical processes that occur in freshwater under anthropogenic eutrophication could lead to myriad shifts in nitrogen (N):phosphorus (P) stoichiometry in global freshwater ecosystems, but this is not yet well-assessed. Here we evaluated the characteristics of N and P stoichiometries in bodies of freshwater and their herbaceous macrophytes across human-impact levels, regions and periods. Freshwater and its macrophytes had higher N and P concentrations and lower N:P ratios in heavily than lightly human-impacted environments, further evidenced by spatiotemporal comparisons across eutrophication gradients. N and P concentrations in freshwater ecosystems were positively correlated and N:P was negatively correlated with population density in China. These results indicate a faster accumulation of P than N in human-impacted freshwater ecosystems, which could have large effects on the trophic webs and biogeochemical cycles of estuaries and coastal areas by freshwater loadings, and reinforce the importance of rehabilitating these ecosystems.
Summary Stoichiometric rules may explain the allometric scaling among biological traits and body size, a fundamental law of nature. However, testing the scaling of elemental stoichiometry and growth to size over the course of plant ontogeny is challenging. Here, we used a fast‐growing bamboo species to examine how the concentrations and contents of carbon (C), nitrogen (N) and phosphorus (P), relative growth rate ( G ), and nutrient productivity scale with whole‐plant mass ( M ) at the culm elongation and maturation stages. The whole‐plant C content vs M and N content vs P content scaled isometrically, and the N or P content vs M scaled as a general 3/4 power function across both growth stages. The scaling exponents of G vs M and N (and P) productivity in newly grown mass vs M relationships across the whole growth stages decreased as a −1 power function. These findings reveal the previously undocumented generality of stoichiometric allometries over the course of plant ontogeny and provide new insights for understanding the origin of ubiquitous quarter‐power scaling laws in the biosphere.
Aims(i) To explore variations in nutrient resorption of woody plants and their relationship with nutrient limitation and (ii) to identify the factors that control these variations in forests of eastern China.
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