[Effects of Short-Term Nitrogen and Phosphorus Addition on Soil Respiration Components in a Subalpine Grassland of Qilian Mountains].

In order to investigate the effects of short-term nitrogen and phosphorus addition on soil respiration and its components in a subalpine grassland located on the Qilian Mountains, a random block design of nitrogen[10 g·(m2·a)-1, N], phosphorus[5 g·(m2·a)-1, P], nitrogen and phosphorus addition[10 g·(m2·a)-1N and 5 g·(m2·a)-1P, NP], the control (CK), and complete control (CK') was conducted from June to August 2019, and total soil respiration and its component respiration rates were measured. The results showed that nitrogen addition reduced soil total respiration and heterotrophic respiration rates at a lower rate than P addition[-16.71% vs. -19.20%; -4.41% vs. -13.05%], but the rate of decrease in autotrophic respiration was higher than that of P addition (-25.03% vs. -23.36%); N and P mixed application had no significant effect on soil total respiration rate. The total soil respiration rate and its components were significantly exponentially correlated with soil temperature, and the temperature sensitivity of soil respiration rate was decreased by nitrogen addition (Q10:-5.64%-0.00%). P increased Q10 (3.38%-6.98%), and N and P reduced autotrophic respiration rate but increased heterotrophic respiration rate Q10 (16.86%) and decreased total soil respiration rate Q10 (-2.63%- -2.02%). Soil pH, soil total nitrogen, and root phosphorus content were significantly correlated with autotrophic respiration rate (P<0.05) but not with heterotrophic respiration rate, and root nitrogen content was significantly negatively correlated with heterotrophic respiration rate (P<0.05). In general, autotrophic respiration rate was more sensitive to N addition, whereas heterotrophic respiration rate was more sensitive to P addition. Both N and P addition significantly reduced soil total respiration rate, whereas N and P mixture did not significantly affect soil total respiration rate. These results can provide a scientific basis for the accurate assessment of soil carbon emission in subalpine grassland.

[Distribution of fine root biomass of main planting tree species in Loess Plateau, China].

The distribution of fine roots of Pinus tabuliformis, Populus tomentosa, Prunus armeniaca, Robinia pseudoacacia, Hippophae rhamnoides, and Caragana korshinskii was investigated by using soil core method and the fine root was defined as root with diameter less than 2 mm. The soil moisture and soil properties were measured. The results showed that in the horizontal direction, the distribution of fine root biomass of P. tabuliformis presented a conic curve, and the fine root biomass of the other species expressed logarithm correlation. Radial roots developed, the fine root biomass were concentrated within the scope of the 2-3 times crown, indicating that trees extended their roots laterally to seek water farther from the tree. In the vertical direction, the fine root biomass decreased with the increasing soil depth. Fine root biomass had significant negative correlation with soil water content and bulk density, while significant positive correlation with organic matter and total N contents.