Ecosystem processes in semiarid grasslands. II.* Litter production decomposition and nutrient dynamics

Abstract

Changes in tissue nutrient concentration and nutrient uptake of a C3 native grassland and a sown C4 buffel grassland community, growing on infertile sandy red earth soils near Charleville, were studied. The seasonal pattern of litter production of grasslands in the grazed and ungrazed situation was also investigated. Studies in litter decomposition of Mitchell grass are reported. The decline in the above-ground biomass growth rate of both communities over the summer growing period corresponded with a similar trend in the uptake of nitrogen and phosphorus. Moreover, tissue shoot phosphorus concentrations of all perennial grass species were always low. The total amount of nutrient absorbed (nitrogen, phosphorus) was about 35% greater for the buffel compared with the native grassland community. Both communities could be contrasted with respect to the efficiency of nutrient absorption and nutrient utilization. Continued overgrazing led to a reduction in litter and root yield. As little biomass was produced by the community over the autumn-winter period, the litter production rate could be expressed as a function of herbage yield at the commencement of the period and was found to be relatively independent of grazing pressure. The agronomic and ecological implications of these results are discussed in relation to the management of these grasslands. __________________ *Part I, Aust. J. Agric. Res., 29: 773 (1978).

Response of a perennial grassland to nitrogen and phosphorus additions in sub-tropical, semi-arid Australia

“…1). This is also true for perennial grasses elsewhere in Australia (Norman, 1963;Christie, 1979;Friedel, 1981) but contrary to Turner's (1998a, b) finding that N : P ratios in annual grasslands changed from assumed P-limitation (14-17) to N and P co-limitation (9-10) between years according to effects of seasonal rainfall patterns on N availability. Much of the discrepancy may be attributed to a greater dependence of annual grasses on the highly variable pools of available nutrients in soil compared with the buffered supply (via retranslocation from plant stores) available to perennials.…”

“…Moreover, many studies reported N : P ratios on a whole-plant or community basis rather than a plant component basis (Table 2). While this is consistent with the method of Koerselman and Meuleman (1996), data from the present and other studies of semi-arid grasslands (Norman, 1963;Christie, 1979;Friedel, 1981) demonstrate that N:P ratios vary between aboveground components in the order: litter'standing dead'green foliage'culms (e.g. Fig.…”

“…Few trials included P-only additions (Table 2) but the available data suggest that P and N were co-limiting at plant ratios between 8 and 18 (Norman, 1962;Tupper, 1978). At four locations throughout semi-arid Australia (Christie, 1979;Silcock et al, 1985;Holm & Allen, 1988;Rice et al, 1994), ratios greater than 18 suggest some potential for P limitation of perennial grasses. Unfortunately, N and P concentrations (and full climatic and environmental variables) have been reported for few fertilizer trials and so more definitive identification of 'critical' N : P ratios for semi-arid grasslands remains elusive.…”

The significance of termites as decomposers in contrasting grassland communities of semi-arid eastern Australia

“…Using nylon-mesh litter bags anchored to the soil surface, Christie (1979) followed the decomposition of current season's litter produced by mitchell grass (Astrebla spp. ), a C 4 species widespread throughout the grasslands of western Queensland.…”

Influence of Management on Soil Organic Carbon Dynamics in Northern Mixed-Grass Rangeland

“…Studies have shown that grazing affects SOC levels, either through changes in plant community (Coupland et al, 1960;Dormaar and Willms, 1990;Coupland, 1992) or by other more subtle and less discernable responses such as litter accumulation and decomposition rates, changes in chemical composition of soil organic matter (SOM), amount and quality of root exudates, increased root biomass, and more rapid cycling of C (Schuster, 1964;Smoliak et al, 1972;Dyer and Bokhari, 1976;Davidson, 1978;Christie, 1979;Detling et al, 1979;Holland and Detling, 1990;Naeth et al, 1991;Shariff et al, 1994;Ganjegunte et al, 2005). The quantity and chemical composition of SOM is important to C and N cycling, as N is often the limiting factor to productivity in rangeland ecosystems (Power, 1994).…”