[Applicability of five drought indices for agricultural drought evaluation in Jilin Province, China.] / 5种干旱指数在吉林省农业干旱评估中的适用性.

Drought is a severe meteorological disaster on agriculture in Jilin Province. Agricultural drought can be represented by drought indices, but there is no universal applicable index. It is of great significance to examine the applicability of drought indices for agricultural drought evaluation. Based on daily meteorological data, soil moisture data, and drought statistical information from 1961 to 2014, we selected typical drought years and typical drought zones. The applicability of five drought indices was evaluated, including precipitation anomaly percentage (PA), relative moisture index (MI), crop water deficit anomaly index (CWDIa), Palmer drought severity index (PDSI) and meteorological drought comprehensive index (MCI). The results showed that agricultural drought evaluation of MI was consistent best with drought information for two typical drought years of 1997 and 2007, followed by PA and MCI. For typical drought zones (Tongyu in the west, Lishu in the center and Helong in the east), MI and PDSI performed much better than other ones. During growing season, PA was more applicable in April, July and August, MI was applicable to April, May and September, CWDIa only performed well in May, PDSI could be an indicator to agricultural drought in June, July, August and September, MCI was useful in May, June, July and August. For different regions with agricultural drought, MI, PDSI and MCI were applicable in western region, PDSI in central region, and PA, PDSI and MCI were suitable for eastern region.

[Factors influencing the spatial variability in soil respiration under different land use regimes].

In order to investigate the factors influencing the spatial variability in soil respiration under different land use regimes, field experiments were performed. Soil respiration and relevant environment, vegetation and soil factors were measured. The spatial variability in soil respiration and the relationship between soil respiration and these measured factors were investigated. Results indicated that land use regimes had significant effects on soil respiration. Soil respiration varied significantly (P < 0.001) among different land use regimes. Soil respiration rates ranged from 1.82 to 7.46 micromol x (m2 x s)(-1), with a difference of 5.62 micromol x (m2 x s)(-1) between the highest and lowest respiration rates. Soil organic carbon was a key factor controlling the spatial variability in soil respiration. In all, ecosystems studied, the relationship between soil respiration and soil organic carbon content can be described by a power function. Soil respiration increased with the increase of soil organic carbon. In forest ecosystem, the relationship between soil respiration and diameter at breast height (DBH) of trees can be explained by a natural logarithmic function. A model composed of soil organic carbon (C, %), available phosphorous (AP, g x kg(-1)) and diameter at breast height (DBH, cm) explained 92.8% spatial variability in soil respiration for forest ecosystems.

[Effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation].

This study was aimed to investigate the effects of simulated warming on soil respiration in a cropland under winter wheat-soybean rotation. Randomized experiments were carried out in the cropland. 6 Plots were arranged and there were 2 treatments, simulated warming and control. A portable soil CO2 fluxes system (LI-8100) was used to measure soil respiration rates. Soil CO2 production rates were determined by using a Barometric Process Separation (BaPS) method. Soil temperature and soil moisture were simultaneously determined when measuring soil respiration rates. Results indicated that soil respiration rates in different treatments showed similar seasonal variability, in accordance with the variability in soil temperature. Seasonal mean soil respiration rates for simulated warming and control treatments were 3.54 and 2.49 micromol x (m2 x s)(-1), respectively, during the winter wheat growth season, while they were 4.80 and 4.14 micromol x (m2 x s)(-1), respectively, during the soybean growth season. Simulated warming significantly (P < 0.05) enhanced soil respiration during both the winter wheat and soybean growth seasons. The impact of simulated warming on soil respiration was particularly obvious during the later growth stages of winter wheat (from heading to maturity stages) and soybean (from flowing to maturity stages). Further investigations suggested that, for both the winter wheat and soybean growth seasons, the relationship between soil respiration and soil temperature could be well explained (P < 0.01) by exponential functions. The temperature sensitivity (Q10) of soil respiration in the simulated warming treatments was significantly higher than that in the control treatments. The Q10 values for the simulated warming and control treatments were 1.83 and 1.26, respectively, during the winter wheat growth season, while they were 2.85 and 1.70, respectively, during the soybean growth season. This study showed that simulated warming significantly increased soil respiration in the cropland.