Increase In Aboveground Production Research Articles

Shifting grassland plant community structure drives positive interactive effects of warming and diversity on aboveground net primary productivity.

Ecosystems worldwide are increasingly impacted by multiple drivers of environmental change, including climate warming and loss of biodiversity. We show, using a long-term factorial experiment, that plant diversity loss alters the effects of warming on productivity. Aboveground primary productivity was increased by both high plant diversity and warming, and, in concert, warming (≈1.5 °C average above and belowground warming over the growing season) and diversity caused a greater than additive increase in aboveground productivity. The aboveground warming effects increased over time, particularly at higher levels of diversity, perhaps because of warming-induced increases in legume and C4 bunch grass abundances, and facilitative feedbacks of these species on productivity. Moreover, higher plant diversity was associated with the amelioration of warming-induced environmental conditions. This led to cooler temperatures, decreased vapor pressure deficit, and increased surface soil moisture in higher diversity communities. Root biomass (0-30 cm) was likewise consistently greater at higher plant diversity and was greater with warming in monocultures and at intermediate diversity, but at high diversity warming had no detectable effect. This may be because warming increased the abundance of legumes, which have lower root : shoot ratios than the other types of plants. In addition, legumes increase soil nitrogen (N) supply, which could make N less limiting to other species and potentially decrease their investment in roots. The negative warming × diversity interaction on root mass led to an overall negative interactive effect of these two global change factors on the sum of above and belowground biomass, and thus likely on total plant carbon stores. In total, plant diversity increased the effect of warming on aboveground net productivity and moderated the effect on root mass. These divergent effects suggest that warming and changes in plant diversity are likely to have both interactive and divergent impacts on various aspects of ecosystem functioning.

Plant community responses to long-term fertilization: changes in functional group abundance drive changes in species richness

Declines in species richness due to fertilization are typically rapid and associated with increases in aboveground production. However, in a long-term experiment examining the impacts of fertilization in an early successional community, we found it took 14 years for plant species richness to significantly decline in fertilized plots, despite fertilization causing a rapid increase in aboveground production. To determine what accounted for this lag in the species richness response, we examined several potential mechanisms. We found evidence suggesting the abundance of one functional group-tall species with long-distance (runner) clonality-drove changes in species richness, and we found little support for other mechanisms. Tall runner species initially increased in abundance due to fertilization, then declined dramatically and were not abundant again until later in the experiment, when species richness and the combined biomass of all other functional groups (non-tall runner) declined. Over 86 % of the species found throughout the course of our study are non-tall runner, and there is a strong negative relationship between non-tall runner and tall runner biomass. We therefore suggest that declines in species richness in the fertilized treatment are due to high tall runner abundance that decreases the abundance and richness of non-tall runner species. By identifying the functional group that drives declines in richness due to fertilization, our results help to elucidate how fertilization decreases plant richness and also suggest that declines in richness due to fertilization can be lessened by controlling the abundance of species with a tall runner growth form.

Soil respiration and microbial activity in a Mediterranean grassland exposed to Free Air CO2Enrichment (FACE)

The effects of elevated atmospheric CO 2 on in situ soil respiration and belowground biomass were studied in a FACE (Free Air CO 2 Enrichment) facility. A Mediterranean grassland community was exposed to elevated and ambient CO 2 concentrations in a mini-FACE system in Tuscany (Italy). We quantified litter mass and chemistry, root growth and turnover, CO 2 efflux from soils, and soil microbial biomass. Elevated CO 2 caused limited increases in aboveground production. Litter quality, fine root turnover, microbial biomass, root growth, and root biomass were not significantly affected by elevated CO 2 , except during some periods. Our results suggest that elevated atmospheric CO 2 might moderately accelerate inputs of organic matter to soil carbon pools in Mediterranean grasslands, but it may also partially accelerate losses of carbon from belowground by stimulating soil respiration.

Nitrogen deposition but not ozone affects productivity and community composition of subalpine grassland after 3 yr of treatment

A field experiment was established at 2000 m above sea level (asl) in the central Swiss Alps with the aim of investigating the effects of elevated ozone (O(3)) and nitrogen deposition (N), and of their combination, on above-ground productivity and species composition of subalpine grassland. One hundred and eighty monoliths were extracted from a species-rich Geo-Montani-Nardetum pasture and exposed in a free-air O(3)-fumigation system to one of three concentrations of O(3) (ambient, 1.2 x ambient, 1.6 x ambient) and five concentrations of additional N. Above-ground biomass, proportion of functional groups and normalized difference vegetation index (NDVI) were measured annually. After 3 yr of treatment, the vegetation responded to the N input with an increase in above-ground productivity and altered species composition, but without changes resulting from elevated O(3). N input > 10 kg N ha(-1) yr(-1) was sufficient to affect the composition of functional groups, with sedges benefiting over-proportionally. No interaction of O(3) x N was observed, except for NDVI; positive effects of N addition on canopy greenness were counteracted by accelerated leaf senescence in the highest O(3) treatment. The results suggest that effects of elevated O(3) on the productivity and floristic composition of subalpine grassland may develop slowly, regardless of the sensitive response to increasing N.

Distribution and cycling of macronutrients in a Pinusresinosa plantation fertilized with nitrogen and potassium

Fertilization with 100 kg K ha−1 as KCl and 100 kg N ha−1 as NH4NO3 resulted in an 11% increase in aboveground biomass and a 32% increase in aboveground production 4 years following fertilization of a 33-year-old red pine (Pinusresinosa Ait.) plantation in central Wisconsin. The greatest absolute increase in dry matter occurred in the foliage, followed by the sapwood and the live branches. Fertilization increased all macronutrients (N, P, K, Ca, Mg) in the aboveground tissues. The increase was greatest for N, followed by Ca, K, Mg, and P. The net gains in macronutrients in the live branches and the sapwood were due not only to increases in dry matter production but also to increases in nutrient concentrations. However, the increases in macronutrients in the foliage were related to an increase in foliage mass rather than to changes in foliar concentrations. Whereas 26 kg K ha−1 (26% of applied K) was recovered in the biomass and forest floor 4 years after fertilization, 107 kg N ha−1 (107% of applied N) was recovered in these pools. The greater recovery of N than the amount applied was attributed to additive errors associated with preparation of nutrient budgets. Fertilization increased leaching losses of all macronutrients, especially [Formula: see text] and Ca2+, at the bottom of the rooting zone. However, leaching losses returned to levels measured in the control stand within 5 [Formula: see text] to 14 months [Formula: see text] following fertilization.