Influence of light intensity on the distribution of carbon and consequent effects on mineralization of soil nitrogen in a barley (Hordeum vulgare L.)-soil system

Abstract

A pot experiment was conducted in a 14C-labelled atmosphere to study the influence of living plants on organic-N mineralization. The soil organic matter had been labelled, by means of a 200-days incubation, with 15N. The influence of the carbon input from the roots on the formation of microbial biomass was evaluated by using two different light intensities (I). Mineralization of 15N-labelled soil N was examined by following its fate in both the soil biomass and the plants. Less dry matter accumulated in shoots and roots at the lower light intensity. Furthermore, in all the plant-soil compartments examined, with the exception of rhizosphere respiration, the proportion of net assimilated t4C was lower in the low-I treatment than in the high-I treatment. The lower rates of ~4C and 15N incorporation into the soil biomass were associated with less root-derived ~4C. During the chamber period (~4CO2-atmosphere), mineralized amounts of ~SN (measured as plant uptake of ~SN) were small and represented about 6.8 to 7.8% of the initial amount of organic 15N in the soil. Amounts of unlabelled N found in the plants, as a percentage of total soil N, were 2.5 to 3.3%. The low availability of labelled N to microorganisms was the result of its stabilization during the 210 days of soil incubation. Differences in carbon supply resulted in different rates of N mineralization which is consistent with the hypothesis that roots induce N mineralization. N mineralization was higher in the high-I treatment. On the other hand, the rate of mineralization of unlabelled stable soil N was lower than labelled soil ~SN which was stabilized. The amounts of 15N mineralized in planted soil during the chamber period (43 days) which were comparable with those mineralized in unplanted soil incubated for 210 days, also suggested that living plants increased the turnover rate of soil organic matter.

C and N allocation in soil under ryegrass and alfalfa estimated by 13C and 15N labelling

“…The growth after shading is restricted by low assimilation rates (Shipley 2002), which also reduces the demand for N in the shoots. Moreover, under shaded conditions a reduced rhizodeposition causes a decreased turnover of the microbial biomass and SOM and, thus, a lower N mineralization (Zagal 1994). In our study no change of the 13 C recovery in the soil of both plants and no change of the 15 N recovery in the shoots of L. perenne was observed after shading.…”

Increases in nitrogen uptake rather than nitrogen-use efficiency support higher rates of temperate forest productivity under elevated CO 2

“…46). Because SOM contains N, the delivery of plant-derived substrates can also stimulate a more rapid mineralization of N from SOM (47)(48)(49)(50)(51). Rapid plant growth under elevated CO 2 is associated with greater hyphal length and fungal activity in the soil and an increase in the degree to which fine roots are colonized by ectoand arbuscular mycorrhizal fungi (36,52,53).…”

Review: Factors affecting rhizosphere priming effects

“…The direct methods estimate either C org changes or differences in mineral nutrients, mainly N, before and after cultivation and compare these changes with that of the fallow soil samples for the same investigation period. Simultaneous measurements of both (C org and N min ) were used very seldom (Sallih et al, 1987;Billes et al, 1988;Zagal, 1994). High variability of C org content and its very low changes during short-term experiments decrease the applicability of direct methods.…”

“…Up to now, only few studies have investigated the effect of photosynthesis on below-ground processes and C turnover in the rhizosphere. They have shown that the intensity of photosynthesis is the main factor controlling below-ground C allocation, exudation, as well as CO 2 efflux from the soil (Whipps, 1984;Zagal, 1994;Todorovic et al, 1999;Craine et al, 1999;Högberg et al, 2001;Kuzyakov and Cheng, 2001). An increase in the total CO 2 efflux from the soil with using plants growing under better light conditions was observed in all these studies.…”