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Soil N Availability (soil + n_availability)

Distribution by Scientific Domains

Life Sciences	75%

Selected Abstracts

CO2 and nitrogen, but not population density, alter the size and C/N ratio of Phytolacca americana seeds

FUNCTIONAL ECOLOGY, Issue 3 2005
J.-S. HE
Summary 1Plants can provision seeds by optimizing seed size, number and nutrient content to maximize parental fitness. According to the McGinley,Charnov hypothesis, seed size should be determined by the ratio of carbon to nitrogen (C/N) available to the plant, with larger seed size correlating with larger C/N ratios and smaller absolute N content. 2This hypothesis was tested by establishing monocultures of Phytolacca americana L. (Phytolaccaceae) at three population densities under ambient and elevated CO2 environments, with two availabilities of soil N. 3Elevated CO2 reduced both seed size and N concentration while increasing the C/N ratio; high soil N availability produced the opposite result for N concentration and C/N ratio. Higher planting densities reduced plant biomass, but did not alter seed size. 4In accordance with the McGinley,Charnov hypothesis, larger seeds had both larger C/N ratios and smaller N content. However, the increase in C/N ratio caused by elevated CO2 corresponded with smaller seeds overall: elevated CO2 reduced seed size, although the seed size,C/N relationship remained positive. 5These results suggest an alternative mechanism to explain variation in seed size, and suggest that future climate conditions may alter seed quality and plant reproductive behaviour. [source]

Changes in soil nitrogen availability due to stand development and management practices on semi-arid sandy lands, in northern China

LAND DEGRADATION AND DEVELOPMENT, Issue 5 2009
F. S. Chen
Abstract Soil nitrogen (N) availability is one of the limiting factors for plant growth on sandy lands. Little is known about impacts of afforestation on soil N availability and its components in southeastern Keerqin sandy lands, China. In this study, we measured N transformation under sandy Mongolian pine (Pinus sylvestris var. mongolica Litv.) plantations of different ages (grassland, young, middle-aged, close-to-mature) and management practices (non-grazing and free-grazing) during the growing seasons using the ion exchange resin bag method. Results showed that, for all plots and growing season, soil NH -N, NO -N, mineral N, and relative nitrification index, varied from 0·18 to 1·54, 0·96 to 22·05, 1·23 to 23·58,µg,d,1,g,1 dry resin, and 0·76 to 0·97, respectively, and NO -N dominated the available N amount due to intense nitrification in these ecosystems. In general, the four indices significantly increased in the oldest plantation, with corresponding values in non-grazing sites lower than those in free-grazing sites (p,<,0·05). Our studies indicated that it is a slow, extended process to achieve improvement in soil quality after afforestation of Mongolian pine in the study area. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Cross-site comparison of herbivore impact on nitrogen availability in grasslands: the role of plant nitrogen concentration

OIKOS, Issue 11 2009
E. S. Bakker
Herbivores may influence the nitrogen (N) recycling rates and consequently increase or decrease the productivity of grasslands. Plant N concentration emerged as a critical parameter to explain herbivore effects from several conceptual models, which predict that herbivores decrease soil N availability when plant N concentration is low whereas they increase it when plant N concentration is high (Hobbs 1996, Ritchie et al. 1998, Pastor et al. 2006). However, a broader cross-site comparison among published studies to test these predictions is hampered by the different methodologies used to measure soil N availability or a proxy thereof, and a lack of measurements of plant N concentration. Therefore it remains unclear whether these model predictions are generally valid across a range of grasslands. We tested whether there is a relationship between plant N concentration and herbivore impact on soil N availability (measured with resin bags) with a study of replicate 6,8,year old exclosures (with an unfenced control) of vertebrate herbivores (>1,kg) established at each of seven grassland sites in North America and Europe. Contrary to model predictions, we found a negative relationship between the effect of herbivores on resin bag soil N availability and plant N concentration. Our study confirms the importance of plant N concentration as a predictor of herbivore effect on soil N availability across grasslands, but contradicts the models. A possible explanation may be that the results represent a transient situation as the exclosures were relatively young whereas the models may refer to an equilibrium state. Simultaneous measurements of both plant N concentration and herbivore effect on soil N availability from more grassland sites, preferably with contrasting plant N concentrations and including exclosures of different ages, should resolve the contrast between model predictions and our field measurements. [source]