Drought drives rapid shifts in tropical rainforest soil biogeochemistry and greenhouse gas emissions.

Climate change models predict more frequent and severe droughts in the humid tropics. How drought will impact tropical forest carbon and greenhouse gas dynamics is poorly understood. Here we report the effects of the severe 2015 Caribbean drought on soil moisture, oxygen, phosphorus (P), and greenhouse gas emissions in a humid tropical forest in Puerto Rico. Drought significantly decreases inorganic P concentrations, an element commonly limiting to net primary productivity in tropical forests, and significantly increases organic P. High-frequency greenhouse gas measurements show varied impacts across topography. Soil carbon dioxide emissions increase by 60% on slopes and 163% in valleys. Methane (CH4) consumption increases significantly during drought, but high CH4 fluxes post-drought offset this sink after 7 weeks. The rapid response and slow recovery to drought suggest tropical forest biogeochemistry is more sensitive to climate change than previously believed, with potentially large direct and indirect consequences for regional and global carbon cycles.

Perennial grasslands enhance biodiversity and multiple ecosystem services in bioenergy landscapes.

Agriculture is being challenged to provide food, and increasingly fuel, for an expanding global population. Producing bioenergy crops on marginal lands--farmland suboptimal for food crops--could help meet energy goals while minimizing competition with food production. However, the ecological costs and benefits of growing bioenergy feedstocks--primarily annual grain crops--on marginal lands have been questioned. Here we show that perennial bioenergy crops provide an alternative to annual grains that increases biodiversity of multiple taxa and sustain a variety of ecosystem functions, promoting the creation of multifunctional agricultural landscapes. We found that switchgrass and prairie plantings harbored significantly greater plant, methanotrophic bacteria, arthropod, and bird diversity than maize. Although biomass production was greater in maize, all other ecosystem services, including methane consumption, pest suppression, pollination, and conservation of grassland birds, were higher in perennial grasslands. Moreover, we found that the linkage between biodiversity and ecosystem services is dependent not only on the choice of bioenergy crop but also on its location relative to other habitats, with local landscape context as important as crop choice in determining provision of some services. Our study suggests that bioenergy policy that supports coordinated land use can diversify agricultural landscapes and sustain multiple critical ecosystem services.

Initial nitrous oxide, carbon dioxide, and methane costs of converting conservation reserve program grassland to row crops under no-till vs. conventional tillage.

Around 4.4 million ha of land in USDA Conservation Reserve Program (CRP) contracts will expire between 2013 and 2018 and some will likely return to crop production. No-till (NT) management offers the potential to reduce the global warming costs of CO2 , CH4 , and N2 O emissions during CRP conversion, but to date there have been no CRP conversion tillage comparisons. In 2009, we converted portions of three 9-21 ha CRP fields in Michigan to conventional tillage (CT) or NT soybean production and reserved a fourth field for reference. Both CO2 and N2 O fluxes increased following herbicide application in all converted fields, but in the CT treatment substantial and immediate N2 O and CO2 fluxes occurred after tillage. For the initial 201-day conversion period, average daily N2 O fluxes (g N2 O-N ha(-1)  d(-1) ) were significantly different in the order: CT (47.5 ± 6.31, n = 6) â‰« NT (16.7 ± 2.45, n = 6) â‰« reference (2.51 ± 0.73, n = 4). Similarly, soil CO2 fluxes in CT were 1.2 times those in NT and 3.1 times those in the unconverted CRP reference field. All treatments were minor sinks for CH4 (-0.69 ± 0.42 to -1.86 ± 0.37 g CH4 -C ha(-1)  d(-1) ) with no significant differences among treatments. The positive global warming impact (GWI) of converted soybean fields under both CT (11.5 Mg CO2 e ha(-1) ) and NT (2.87 Mg CO2 e ha(-1) ) was in contrast to the negative GWI of the unconverted reference field (-3.5 Mg CO2 e ha(-1) ) with on-going greenhouse gas (GHG) mitigation. N2 O contributed 39.3% and 55.0% of the GWI under CT and NT systems with the remainder contributed by CO2 (60.7% and 45.0%, respectively). Including foregone mitigation, we conclude that NT management can reduce GHG costs by ~60% compared to CT during initial CRP conversion.

[Soil N2O flux and its affecting factors under different land use patterns in Three Gorges Reservoir Area of China].

By using static chamber techniques, the N2O emission from soils under different land use patterns was measured. The results showed that the N2O flux ranged from -21 to 435 microg x m(-2) h(-1), and the annual N2O flux was decreased in the order of vegetable field > orchard > upland > upland transferred from paddy field > woodland, being 447.14, 313.57, 167.00, 124.875 and 7.24 mg x m(-2), respectively. The N2O flux presented significant seasonal fluctuation, with the maximum in spring and summer, followed by in autumn, and the minimum in winter, which was approximately consistent with the changes of air- and soil temperature. N2O flux had significant positive correlation with the soil temperature at 5 cm depth and soil NO3(-)-N content, but no significant correlation with soil moisture and NH4(+)-N contents.

[Variations and influencing factors of nitrate nitrogen concentration in water in a small watershed of Three Gorges area].

In order to study the water quality and response to influencing factors in typical watersheds of Three Gorges area between 2004 and 2005, the variation characteristics of nitrate nitrogen concentration were analyzed under heterogeneous landscape condition through continuous observation with method of dividing into sub-watersheds in Quxi watershed (the first-grade branch, located in Three Gorges). The results suggested that nitrate nitrogen concentration fluctuated between 0.4 and 14.6 mg x L(-1) with the highest in winter,higher in autumn and summer and lower in spring. Discrepancy also exists in different years. In addition, nitrate nitrogen concentration shows increasing trends with the aggravating impacts of agricultural activities on environment. Moreover, nitrate nitrogen concentration had some relationships with different land use types and space layout to some extent, and was also affected by geological and hydrological characters in the sub-watersheds, which indicated that response of nitrate nitrogen concentration in water was evident to influencing factors.

[CO2 fluxes from red soil under four land use types in mid-subtropical, China].

CO2 fluxes from red soil under different land use (paddy, upland, woodland and orchard) were measured at Xianning city, Hubei province with closed chamber method. The results showed that the annual CO2 emission were 1129, 632, 533, and 828 g/(m2 a) for paddy, upland, woodland, and orchard respectively. Soil CO2 fluxes revealed seasonal fluctuations, with the tendency that maximum value was in summer, minimum was in winter and intermediate in spring and autumn except for paddy soil. CO2 fluxes for paddy soil were significantly higher than the other soils except it was submerged. An exponential relationship between soil CO2 fluxes and soil temperature at 5cm depth could be received. Air temperature also had significant positive correlation with soil CO2 fluxes except for paddy soil. The Q10 values were 1.51 (paddy), 1.88(orchard), 2.08(woodland), 2.7(upland) respectively based on the exponential equation between soil CO2 fluxes and soil temperature. The results indicated that there was no significant correlation between CO2 fluxes and soil moisture. In addition, DOC had the same seasonal tendency as CO2 fluxes, and it increased when soil was irrigated or rained.