Asymmetric response of aboveground and belowground temporal stability to nitrogen and phosphorus addition in a Tibetan alpine grassland.

Anthropogenic eutrophication is known to impair the stability of aboveground net primary productivity (ANPP), but its effects on the stability of belowground (BNPP) and total (TNPP) net primary productivity remain poorly understood. Based on a nitrogen and phosphorus addition experiment in a Tibetan alpine grassland, we show that nitrogen addition had little impact on the temporal stability of ANPP, BNPP, and TNPP, whereas phosphorus addition reduced the temporal stability of BNPP and TNPP, but not ANPP. Significant interactive effects of nitrogen and phosphorus addition were observed on the stability of ANPP because of the opposite phosphorus effects under ambient and enriched nitrogen conditions. We found that the stability of TNPP was primarily driven by that of BNPP rather than that of ANPP. The responses of BNPP stability cannot be predicted by those of ANPP stability, as the variations in responses of ANPP and BNPP to enriched nutrient, with ANPP increased while BNPP remained unaffected, resulted in asymmetric responses in their stability. The dynamics of grasses, the most abundant plant functional group, instead of community species diversity, largely contributed to the ANPP stability. Under the enriched nutrient condition, the synchronization of grasses reduced the grass stability, while the latter had a significant but weak negative impact on the BNPP stability. These findings challenge the prevalent view that species diversity regulates the responses of ecosystem stability to nutrient enrichment. Our findings also suggest that the ecological consequences of nutrient enrichment on ecosystem stability cannot be accurately predicted from the responses of aboveground components and highlight the need for a better understanding of the belowground ecosystem dynamics.

Understanding Responses of Soil Microbiome to the Nitrogen and Phosphorus Addition in Metasequoia glyptostroboides Plantations of Different Ages.

Nitrogen (N) and phosphorus (P) have significant effects on soil microbial community diversity, composition, and function. Also, trees of different life stages have different fertilization requirements. In this study, we designed three N additions and three P levels (5 years of experimental treatment) at two Metasequoia glyptostroboides plantations of different ages (young, 6 years old; middle mature, 24 years old) to understand how different addition levels of N and P affect the soil microbiome. Here, the N fertilization of M. glyptostroboides plantation land (5 years of experimental treatment) significantly enriched microbes (e.g., Lysobacter, Luteimonas, and Rhodanobacter) involved in nitrification, denitrification, and P-starvation response regulation, which might further lead to the decreasing in alpha diversity (especially in 6YMP soil). The P addition could impact the genes involved in inorganic P-solubilization and organic P-mineralization by increasing soil AP and TP. Moreover, the functional differences in the soil microbiomes were identified between the 6YMP and 24YMP soil. This study provides valuable information that improves our understanding on the effects of N and P input on the belowground soil microbial community and functional characteristics in plantations of different stand ages.

Anatomical responses of leaf and stem of Arabidopsis thaliana to nitrogen and phosphorus addition.

Nitrogen (N) and phosphorus (P) availabilities play crucial roles in plant morphogenesis and physiological processes, but how plant anatomical traits respond to the N and P supply is not well elucidated. We evaluated the effects of N and P supply on multiple leaf and stem anatomical traits of Arabidopsis thaliana. The addition of N increased the stem diameter, cortex thickness, rosette radius, midrib thickness, and size of leaf and stem vasculature significantly. Abaxial stomatal length (LSL) increased while adaxial epidermal cell density decreased significantly with increasing N supply. P addition did not affect stem size and leaf epidermal traits, but enhanced the thickness of stem xylem. The nutrient limiting status did not affect most traits except for LSL. The anatomical traits measured varied a lot in the extent of response to N and P addition, despite relatively stronger response to N addition overall. Cortex thickness, rosette radius, stomatal density and epidermal cell density exhibited relatively high plasticity to both nutrients, while stomatal length and stomatal index were relatively stable. Thus, these results suggested that the anatomical traits of shoot vasculature of A. thaliana were enhanced by both nutrients but more affected by N addition, satisfying the plant growth and nutrient requirements. Our findings may help shed light on plant adaptation to nutrient availability changes under the ongoing anthropogenic impacts, but the generality across numerous plant species still warrants further researches.

Root growth characteristics and antioxidant system of Suaeda salsa in response to the short-term nitrogen and phosphorus addition in the Yellow River Delta.

Human activities have increased nitrogen (N) and phosphorus (P) inputs to the Yellow River Delta and the supply level of N and P affects plant growth as well as ecosystem structure and function directly. However, the root growth, stoichiometry, and antioxidant system of plants in response to N and P additions, especially for herbaceous halophyte in the Yellow River Delta (YRD), remain unknown. A field experiment with N addition (0, 5, 15, and 45 g N m-2 yr-1, respectively) as the main plot, and P addition (0 and 1 g N m-2 yr-1, respectively) as the subplot, was carried out with a split-plot design to investigate the effects on the root morphology, stoichiometry, and antioxidant system of Suaeda salsa. The results showed that N addition significantly increased the above-ground and root biomass as well as shoot-root ratio of S. salsa, which had a significant interaction with P addition. The highest biomass was found in the treatment with 45 g N m-2 yr-1 combined with P addition. N addition significantly increased TN content and decreased C:N ratio of root, while P addition significantly increased TP content and decreased C:P ratio. The main root length (MRL), total root length (TRL), specific root length (SRL), and root tissue density (RTD) of S. salsa root were significantly affected by N addition and P addition, as well as their interaction. The treatments with or without P addition at the 45 g N m-2 yr-1 of N addition significantly increased the superoxide dismutase (SOD), peroxidase (POD), catalase (CAT) activities and soluble protein content of roots, decreased malondialdehyde (MDA) content. And there was a significant interaction between the N and P addition on SOD activity. Therefore, N and P additions could improve the growth of S. salsa by altering the root morphology, increasing the root nutrient content, and stimulating antioxidant system.

Effects of short-term nitrogen and phosphorus addition on soil bacterial community of different halophytes.

Soil microbial community composition and diversity are often affected by nutrient enrichment, which may influence soil microbes to affect nutrient cycling and plant community structure. However, the response of soil bacteria to nitrogen (N) and phosphorus (P) addition and whether it is influenced by plants remains unclear. By 16S rRNA sequencing, we investigated the response of the rhizosphere and bulk soil bacterial communities of different halophytes (salt-rejecting, salt-absorbing, and salt-secreting plant) in the Yellow River Delta to short-term N and P addition. The response of rhizosphere bacterial diversity to N and P addition was opposite in Phragmites communis and Suaeda salsa. N addition increased the rhizosphere soil bacterial α-diversity of S. salsa and Aeluropus sinensis, while P addition decreased the rhizosphere bacterial α-diversity bacteria of S. salsa. The N and P addition had a weak effect on the rhizosphere bacterial community composition and a significant effect on the bulk soil bacterial community composition of halophytes. The S. salsa and P. communis bulk soil bacterial community were mainly influenced by P addition, while it was influenced by N addition in A. sinensis. N and P addition reduced the difference in bacterial community composition between the two types of soil. N and P addition increased the eutrophic taxa (Proteobacteria and Bacteroidetes) and decreased the oligotrophic taxa (Acidobacteria). Redundancy analysis showed that soil organic matter, salt, and total N content had significant effects on the bacterial community composition. The results clarify that the response of soil bacterial communities to N and P additions is inconsistent across the three halophyte soils, and the effect of plant species on the bacterial community was stronger than short-term N and P addition. IMPORTANCE: The bulk soil bacterial community was more affected by nutrient addition. Nitrogen (N) and phosphorus (P) have different effects on bacterial community. Soil organic matter is a key factor influencing the response of bacterial community to nutrient addition. N and P influence on bacterial community changes with plants.

Response of tree growth to nutrient addition is size dependent in a subtropical forest.

Understanding how nutrient addition affects the tree growth is critical for assessing forest ecosystem function and processes, especially in the context of increased nitrogen (N) and phosphorus (P) deposition. Subtropical forests are often considered N-rich and P-poor ecosystems, but few existing studies follow the traditional "P limitation" paradigm, possibly due to differences in nutrient requirements among trees of different size classes. We conducted a three-year fertilization experiment with four treatments (Control, N-treatment, P-treatment, and NP-treatment). We measured soil nutrient availability, leaf stoichiometry, and relative growth rate (RGR) of trees across three size classes (small, medium and large) in 64 plots. We found that N and NP-treatments increased the RGR of large trees. P-treatment increased the RGR of small trees. RGR was mainly affected by N addition, the total effect of P addition was only 10 % of that of N addition. The effect of nutrient addition on RGR was mainly regulated by leaf stoichiometry. This study reveals that nutrient limitation is size dependent, indicating that continuous unbalanced N and P deposition will inhibit the growth of small trees and increase the instability of subtropical forest stand structure, but may improve the carbon sink function of large trees.

[Responses of seedling growth in subtropical secondary broad-leaved forest to nitrogen and phosphorus addition in Jiulian Mountain, China]. / ä¹è¿žå±±æ¬¡ç”Ÿé˜”å¶æž—å¹¼è‹—ç”Ÿé•¿å¯¹æ°®ç£·æ·»åŠ çš„å“åº”.

An experiment with four treatments of control (CK), N addition (100 kg N·hm-2·a-1), P addition (50 kg P·hm-2·a-1) and N + P (100 kg N·hm-2·a-1 + 50 kg P·hm-2·a-1) were conducted to examine the responses of plant height, ground diameter, crown width, specific leaf area, and mortality of seedlings to N and P addition. Under P addition, growth rates of plant height and ground diameter of seedlings decreased significantly by 45.1% and 30.3%, respectively. Fertilization affected the mortality of main constructive tree species. N addition significantly increased seedling mortality of Castanopsis carlesii to 25.1%. Fertilization treatment significantly increased mortality of Castanopsis fargesii to 25.1%-31.3%, while N addition and P addition signi-ficantly reduced mortality of Schima superba and Machilus nanmu. Fertilization significantly decreased the importance value of S. superba and C. fargesii in the seedling community. N addition and P addition significantly increased the importance value of M. nanmu seedling. The combined N and P addition significantly decreased Shannon index and Simpson index of the seedling community. Seedling growth was mainly affected by soil ammonium, available phosphorus, total nitrogen, canopy openness, and specific leaf area. Seedling mortality was mainly affected by soil ammonium, available phosphorus and canopy openness. Synthetically, N and P addition affected seedling growth mainly by regulating soil nitrogen and phosphorus availability and changing leaf functional trait. It accelerated the death of ectomycorrhizal tree species (C. carlesii and C. fargesii), changed the importance value of constructive species in seedling community, reduced species diversity, and ultimately changed community structure of adult trees in subtropical secondary broad-leaved forest.

[Responses of leaf functional traits of dominant plant species in grassland communities to nitrogen and phosphorus addition in loess hilly-gully region.] / é»„åœŸä¸˜é™µåŒºè‰åœ°æ¤è¢«ç¾¤è½ä¼˜åŠ¿ç§å¶ç‰‡åŠŸèƒ½æ€§çŠ¶å¯¹æ°®ç£·æ·»åŠ çš„å“åº”.

To analyze plant functional traits of dominant species to nitrogen and phosphorus addition, three species (Bothriochloa ischaemum, Stipa bungeana, and Lespedeza davurica) were selected in the loess hilly-gully region. A split-plot experiment which included three N treatments (0, 50, and 100 kg N·hm-2·a-1) and three P treatments (0, 40, and 80 kg P2O5·hm-2·a-1) was conducted. At the fast-growing stage, leaf length, leaf width, specific leaf area, leaf dry matter content, leaf N content, leaf P content, and leaf N:P were measured. Results showed that under 50 and 100 kg N·hm-2·a-1 treatments, leaf length and width of B. ischaemum increased significantly by 35.3% and 64.4%, respectively, while only the leaf length of S. bungeana and the leaf width of L. davurica increased significantly by 58.8% and 33.9%, respectively. Leaf dry matter content of the three species decreased significantly by 10.7%, 15.3% and 11.2%, respectively. Leaf N content and N:P of B. ischaemum and S. bungeana increased significantly by 23.0% and 99.2%, 45.8% and 96.9%, respectively, compared with unfertilized treatments. Under 40 and 80 kg P2O5·hm-2·a-1 treatments, leaf length, leaf width and specific leaf area of L. davurica increased significantly by 56.9%, 41.4% and 19.6%, respectively, while leaf dry matter content decreased significantly by 14.9%. Leaf P content of three species increased significantly by 96.7%, 110.9% and 238.4%, while the N:P decreased significantly by 45.8%, 42.8% and 53.7%, respectively, compared with those under unfertilized. Under 50 kg N·hm-2·a-1 treatment, compared with no P application, leaf length and leaf width of L. davurica and leaf P content of the three species significantly increased, and leaf N content of B. ischaemum and S. bungeana decreased significantly at 40 and 80 kg P2O5·hm-2·a-1 treatments. Under 100 kg N·hm-2·a-1 treatment, leaf length of B. ischaemum and S. bungeana, leaf width of L. davurica and leaf P content of three species significantly increased, while leaf N content of B. ischaemum decreased significantly after P application. In summary, functional traits of dominant species showed significant responses to short-term nitrogen and phosphorus addition, with the different responses were mainly related to species traits and fertilization levels. Such difference reflected plant adaptation to habitat changes. The divergent responses of different species to nitrogen and phosphorus addition played an important role in maintaining diversity and stability of grassland communities.

[Effect of nitrogen and phosphorus addition on soil enzyme activities: A meta-analysis]. / æ•´åˆåˆ†æžæ°®ç£·æ·»åŠ å¯¹åœŸå£¤é ¶æ´»æ€§çš„å½±å“.

We conducted a meta-analysis to analyze the effects of nitrogen (N) and combined N and phosphorus (N+P) addition on soil enzyme activities, which being involved in soil carbon (C), N, and P cycles as well as oxidative processes. Nitrogen addition significantly increased the activities of soil C acquisition enzymes, N acquisition enzymes, and P acquisition enzymes by 6.9%, 5.6% and 10.7%, respectively, while the enhancement was much stronger under N+P treatment with 13.4%, 37.4% and 13.3%, respectively. In contrast, both N addition and N+P addition decreased the activities of oxidative enzymes by 6.1% and 0.4%, respectively. The effect sizes of N and N+P addition on soil enzyme activities varied with ecosystem types, N fertilizer types, N addition rates, and the duration of fertilization experiments. Our results suggested that the changes in soil microbes and their enzymes under increasing N deposition and P addition would have profound impacts on soil biogeochemical processes and functions.