[Responses of ecosystem carbon budget to increasing nitrogen deposition in differently degraded Leymus chinensis steppes in Inner Mongolia, China].

Based on a field manipulative nitrogen (N) addition experiment, the effects of atmospheric N deposition level change on the plant biomass and net primary productivity (NPP), soil respiration (Rs) and net ecosystem exchange (NEE) were investigated respectively in 2009 and 2010 in two differently degraded Leymus chinensis steppes in Inner Mongolia of China, and the difference in the response of NEE to equal amount of N addition [10 g x (M2 x a)(-1), MN] between the two steppes was also discussed. The results indicated that for the light degraded Leymus chinensis steppe (site A) , the average plant aboveground biomass (AGB) in MN treatment were 21.5% and 46.8% higher than those of CK in these two years. But for the moderate degraded Leymus chinensis steppe (site B), the N addition decreased the plant AGB and ANPP in 2009, while showed positive effects in 2010. N addition increased the belowground biomass (BGB) of the both sites and belowground NPP (BNPP) of site B in both years, but decreased the BNPP of site A in 2010. The increase of N input in the two steppes did not change the seasonal variation of Rs. The cumulative annual soil C emissions in MN treatment in site A showed an increase of about 14.6% and 25.7% of those in the CK respectively for these two years, while were decreased by about 10.4% and 11.3%, respectively in site B. The NEE of MN treatments, expressed by C, for the two steppes were 59.22 g x (m2 x a)(1) and 166.68 g x (m2 x a)(-1), as well as 83.27 g x (m2 x a)(-1) and 117.47 g x (m2 x a)(-1), respectively in these two years. The increments in NEE originated from N addition for these two years were 15.79 g x (M2 x a)(-1) and 82.94 g x (M2 x a)(-1) in site A and 74.54 g x (M2 x a)(-1) and 101.23 g x (M2 x a)(-1) in site B. The N input per unit could obtain greater C sink effect in the steppe with lower initial N level.

[Reponses of soil total organic carbon and dissolved organic carbon to simulated nitrogen deposition in temperate typical steppe in Inner Mongolia, China].

Based on a field manipulative nitrogen (N) addition experiment, the effects of atmospheric N deposition level change on the contents, inter-annual variation and profile distribution of soil total organic carbon (TOC) and dissolved organic carbon (DOC) were investigated from May, 2008 to October, 2011 in a temperate typical steppe in Inner Mongolia of China, and the relationship between TOC and DOC was also discussed. The treatments in the manipulative experiment included N additions at rates of 0, 5, 10, and 20 g x (m2 x a)(-1), representing the control (CK), low N (LN), medium N (MN), and high N (HN) treatment, respectively. The results indicated that the concentrations of soil TOC and DOC decreased progressively with soil depth in all cases except for the DOC at 10-20 cm depth in individual years. The increase of N input in typical steppe did not change the vertical distribution of soil TOC and DOC, but reduced the vertical variation of TOC and increased the vertical variation of DOC in the surface soil horizon. In addition, the contents of soil TOC and DOC at 0- 10 cm and 10- 20 cm soil layers changed insignificantly after the continuous increase in anthropogenic N input for four years. The soil organic C density of 0-20 cm soil layer for different N treatment levels varied between 3.9 kg x m(-2) and 5.6 kg x m(-2), and the soil organic C densities of fertilized treatments in the first two years were similar to or slightly lower than those of CK, while in the following two years, the increase in N deposition gradually played a positive role in increasing soil organic C density, but the differences in soil TOC and DOC contents between CK and fertilized plots were not significant (P > 0.05). The ratio of soil DOC to TOC (DOC/TOC) varied from 0.32% to 1.09%. The increase in N deposition generally lowered the proportion of DOC in soil TOC, which was conducive to the accumulation of soil organic C. The change of soil DOC was positively correlated with that of TOC (P < 0.01). The temporal variations of soil DOC in different N treatments were all far greater than those of TOC, and the soil DOC was the important sensitive indicator for predicting and evaluating the response of soil C pool to the change in atmospheric N deposition in the temperate grassland ecosystem.

[Eco-hydrological characteristics and soil and water conservation effect of citrus plantation on slope red soil of Jiangxi Province, China].

A 9-year observation was conducted at the experimental plots in the Citrus reticulata plantation in Jiangxi Provincial Eco-Technology Park to study the eco-hydrological characteristics and soil conservation benefits of the plantation on slope red soil. Seven treatments were designed and monitored over nine years. The average flow and the rate of sediment for the seven treatments were reduced by 78.5% and 77.2%, respectively. The reduction rates were the highest in treatments band coverage of Paspalum natatu, whole coverage of P. natatu, and level terrace with grass on ridge, with the values of 94.8%, 94.3% and 92.5%, respectively, followed by in treatment intercropping Glycine max (66.0%) and Raphanus sativus (77.5%), with horizontal planting being better than vertical planting, and the lowest in treatment without understory vegetation (33.1%). The observations on the precipitation redistribution of 43 rainfall events with a mean precipitation of 20.07 mm in 2009-2010 showed that the throughfall, stemflow, and canopy interception were 9.15, 4.72 and 6.20 mm, accounting for 44.7%, 25.7% and 29.6% of the precipitation, respectively. The throughfall and stemflow tended to increase with increasing precipitation. There was a significant liner negative correlation between the canopy interception rate and the precipitation when the rainfall was less than 10 mm, but no significant correlation when the rainfall was greater than 10 mm. The water holding rate of C. reticulata litters was logarithmically correlated with water soaking time, and the maximum water holding rate was 326%. It was considered that rational allocation of understory vegetation played an important role in the soil and water conservation of citrus orchard on slope red soil.