The plasma membrane H⁺-ATPase plays an important role in the plant response to nutrient and environmental stresses. However, the involvement of plant root plasma membrane H⁺-ATPase in adaptation to phosphate (P) starvation is not yet fully elucidated. In this study, experiments were performed with soybean roots in low-P nutrient solution (10 μM). Treatment with fusicoccin, an activator of the plasma membrane H⁺-ATPase, increased P uptake by 35%, while vanadate, an inhibitor of plasma membrane H⁺-ATPase, severely suppressed it. These results suggested that P uptake might be regulated via the modulation of the activity of plasma membrane H⁺-ATPase under P starvation. The relationship between P uptake and the activity of plasma membrane H⁺-ATPase was examined further by using plasma membrane H⁺-ATPase transgenic Arabidopsis thaliana under low-P conditions. Transgenic plants absorbed more P compared with wild-type Arabidopsis. Results from real-time RT-PCR, western-blotting and immunolocalization analysis indicated that the increase in activity of the plasma membrane H⁺-ATPase by P starvation was caused by its transcriptional and translational regulation. A higher expression was observed at the translational level than at the transcriptional level. P starvation could induce a transient increase of endogenous indole-3-acetic acid (IAA) in soybean roots. The exogenous application of IAA stimulated the activity of plasma membrane H⁺-ATPase and P uptake, while naphthylphthalamic acid (NPA), an IAA transport inhibitor, blocked IAA effects. Taken together, these results suggested an involvement of root plasma membrane H⁺-ATPase in the adaptation of soybean to P starvation. IAA might be involved in signal transduction of P starvation by activating the plasma membrane H⁺-ATPase in soybean roots.

Background: Desert steppe, as an ecotone between desert and grassland, has few species and is sensitive to climate change. Climate change alters species diversity and the stability of functional groups, which may positively or negatively affect community stability. However, the response of plant community stability in the desert steppe to experimental warming and increasing precipitation remains largely unexplored.Methods: In a factorial experiment of warming and increasing precipitation for five to seven years (ambient precipitation (P0), ambient precipitation increased by 25% and 50% (P1 and P2), ambient temperature (W0), ambient temperature increased by 2°C and 4°C (W1 and W2)), we estimated the importance value (IV) of four functional groups (perennial grasses, semi-shrubs, perennial forbs and annual herbs), species diversity and community stability.Results: Compared to W0P0, the IV of perennial grasses was reduced by 37.66% in W2P2, whereas the IV of perennial forbs increased by 48.96%. Although increasing precipitation and experimental warming significantly altered species composition, the effect on species diversity was insignificant (P > 0.05). In addition, increasing precipitation and experimental warming had a significant negative impact on community stability. The stability of perennial grasses significantly explained community stability.Conclusion: Our results suggest that the small number of species in desert steppe limits the contribution of species diversity to regulating community stability. By contrast, maintaining high stability of perennial grasses can improve community stability in the desert steppe.

Nitrification plays an important role in nitrogen (N) turnover and N cycling. To date, there have been many studies on the net N turnover in grassland. However, few studies have specifically focused on the gross N turnover, which is mainly due to methodological limitations. Here, we set up an enclosed plot in a desert steppe and determined the gross nitrification (GN) rate of the soil by using the barometric process separation method. We found the seasonal dynamics of the GN in the desert steppe soil, such that the GN in the summer (117.65 ± 24.86 μg N kg⁻¹ h⁻¹) was significantly greater than in the spring and autumn (65.17 ± 7.33 μg N kg⁻¹ h⁻¹), and it peaked in July (213.75 ± 44.66 μg N kg⁻¹ h⁻¹). Additionally, the GN was lowest in the spring, with a means of 50.52 ± 3.95 μg N kg⁻¹ h⁻¹. The seasonal variation in the GN was different than the seasonal variation in the net nitrification rate, and the GN was generally much higher than the net nitrification rate. We further demonstrated that the soil moisture, temperature, bulk density and NH₄⁺-N were the main factors that influenced the seasonal variations in the GN, and that the soil moisture had the greatest impact on the GN among all the factors measured.

Atmogenic sulfur (S) deposition loading by acid rain is one of the biggest environmental problems in China. It is important to know the accumulated S stored in soil, because eventually the size (and also the “desorption” rate) determines how rapidly the soil water pH responds to decrease in S deposition. The S fractions and the ratio of total carbon/total sulfur (C/S) of forest soil in 9 catchments were investigated by comparing soils at the rural and urban sites in China. The S fractions included water-soluble sulfate-S (SO₄-S), adsorbed SO₄-S, insoluble SO₄-S and organic S. The ratio of C/S in soil at the rural site was significantly (p < 0.05) greater than that at the urban site. C/S of soil in the A horizon was significantly (p < 0.05) and negatively correlated with the wet S-deposition rate. The ratio of C/S presents a better indicator for atmogenic S loading. Organic S was the dominant form in soils at rural sites; contributing more than 69% of the total S in the uppermost 30 cm soil. Organic S and adsorbed SO₄-S were the main forms of S in soil at urban sites. High contents of water-soluble SO₄-S and adsorbed SO₄-S were found in uppermost 30 cm soils at urban sites but not at rural sites. Decades of acid rain have caused accumulation of inorganic SO₄-S in Chinese forest soil especially at the urban sites. The soil at urban sites had been firstly acidified, and the impacts on the forest ecosystem in these areas should be noticed.

The impacts of large herbivores on plant communities differ depending on the plants and the herbivores. Few studies have explored how herbivores influence root biomass. Root growth of vegetation was studied in the field with four treatments: sheep grazing alone (SG), cattle grazing alone (CG), mixed grazing with cattle and sheep (MG) and no grazing (CK). Live and total root biomasses were measured using the root ingrowth core and the drilling core, respectively. After 2 years of grazing, total root biomass showed a decreasing trend while live root biomass increased with time during the growing seasons. Belowground net primary production (BNPP) among the treatments varied from 166 ± 32 to 501 ± 88 g m ⁻² and root turnover rates (RTR) varied from 0.25 ± 0.05 to 0.70 ± 0.11 year ⁻¹ . SG had the greatest BNPP and RTR, while the CG had the smallest BNPP and RTR. BNPP and RTR of the MG treatment were between those of the CG and SG treatments. BNPP and RTR of the CK were similar to MG treatment. Compared with other treatments, CG had a greater impact on dominant tall grasses species in communities. SG could decrease community diversity. MG eliminated the disadvantages of single-species grazing and was beneficial to community diversity and stability.