[Role of photosynthesis in regulating soil respiration under nitrogen application in a sandy grassland]. / æ–½æ°®å¤„ç†ä¸‹æ¤ç‰©å ‰åˆå¯¹æ²™è´¨è‰åœ°åœŸå£¤å‘¼å¸çš„è°ƒæŽ§ä½œç”¨.

We examined the role of photosynthesis in regulating soil CO2 emission under nitrogen enrichment in Keerqin sandy grassland. Results showed that nitrogen (N) application could affect soil respiration rate by altering the allocation of photosynthetic products to the belowground. Gross ecosystem photosynthesis rate (GEP) was positively correlated with soil respiration rate (Rs). Nitrogen application reduced slope of the fitting function from 0.236 to 0.161, with the equation intercept difference (0.51 µmol·m-2·s-1) being similar to the nighttime soil respiration rate increment (0.52 µmol·m-2·s-1). From May to October, the difference of photosynthetic rate (differential ratio) caused by nitrogen application was significantly correlated with that of soil respiration (differential ratio). Results from partial correlation confirmed the essential role of photosynthetic rate difference (ΔGEP) in driving soil respiration rate difference (ΔRs) caused by nitrogen application. In the nighttime, soil respiration rate was affected by the aboveground vegetation activities in daytime. The daily mean GEP was an important factor affecting the nighttime soil respiration rate difference (ΔRs) (P<0.01). Photosynthesis, rather than soil temperature, was the main factor affecting soil respiration rate difference (ΔRs) under nitrogen application. Thus, the role of photosynthetic assimilation-regulating may provide a novel supplement for elucidating the responses of soil respiration to nitrogen enrichment.

Altered leaf functional traits by nitrogen addition in a nutrient-poor pine plantation: A consequence of decreased phosphorus availability.

This study aimed to determine how specific leaf area (SLA) and leaf dry matter content (LDMC) respond to N addition and understory vegetation removal in a 13-year-old Mongolian pine (Pinus sylvestris var. mongolica) plantation. Traits (SLA, LDMC, individual needle dry weight, N and P concentrations) of different-aged needles and their crown-average values were measured, and their relationships with soil N and P availability were examined. N addition and understory removal reduced soil Olsen-P by 15-91%. At the crown level, N addition significantly reduced foliar P concentration (by 19%) and SLA (by 8%), and elevated N concentration (by 31%), LDMC (by 10%) and individual leaf dry weight (by 14%); understory removal did not have a significant effect on all leaf traits. At the needle age level, traits of the previous year's needles responded more strongly to N addition and understory removal than the traits of current-year needles, particularly SLA and N concentration. SLA and LDMC correlated more closely with soil Olsen-P than with soil inorganic N, and LDMC correlated more closely with soil Olsen-P than SLA did. These results indicate that aggravated P limitation resulting from N addition and understory removal could constrain Mongolian pine growth through their effects on the leaf traits.

[Effects of nitrogen addition on microbial respiration and root respiration in a sandy grassland.] / æ°®æ·»åŠ å¯¹æ²™è´¨è‰åœ°å¾®ç”Ÿç‰©å‘¼å¸ä¸Žæ ¹ç³»å‘¼å¸çš„å½±å“.

Soil respiration includes root respiration and microbial respiration. Effects of nitrogen addition on root respiration and microbial respiration may be quite different. We examined the effects of N-addition on the releasing of soil CO2 and the responses of root respiration and microbial respiration in a Keerqin sandy grassland, Northeast China. Results showed that both soil respiration and microbial respiration firstly rose then declined during the growing season (May to October). Microbial respiration was the main contributor of soil respiration, accounting for 82.6%. Contribution rate of root respiration altered with months, peaking in May (49.4%) and August (41.9%), with an average contribution rate of 17.4% during the growing season. Root respiration (with a decrease of 17.7%) was more sensitive to N-addition compared with microbial respiration (with a decrease of 3.9%) at 10 ℃. N-addition increased Q10 values of soil respiration and microbial respiration, and enhanced their sensitivity to soil water content variation.

[Effects of nitrogen addition on grassland species diversity and productivity in Keerqin Sandy Land].

Species diversity and productivity are the important indices of the structure and functioning of ecosystems. With Keerqin sandy grassland as test object, this paper studied its species composition, species diversity, and productivity under effects of different level nitrogen (N) addition. Nitrogen addition altered the species composition and the dominant species in the community, increased the vegetation height and coverage, and decreased vegetation light penetration. With the increase of N addition, both the species richness and the diversity decreased. Nitrogen addition increased the aboveground biomass significantly (P<0.01). There was a significant positive relationship between species richness and vegetation light penetration (P<0.01), and a significant negative relationship between species richness and vegetation coverage (P<0.01). It was suggested that nitrogen deposition and artificial nitrogen addition would affect the species composition, species diversity, and productivity of sandy grassland ecosystem.