Responses of wetland graminoids to the relative supply of nitrogen and phosphorus

Abstract

The biomass production of wetland vegetation can be limited by nitrogen or phosphorus. Some species are most abundant in N-limited vegetation, and others in P-limited vegetation, possibly because growth-related traits of these species respond differently to N versus P supply. Two growth experiments were carried out to examine how various morphological and physiological traits respond to the relative supply of N and P, and whether species from sites with contrasting nutrient availability respond differently. In experiment 1, four Carex species were grown in nutrient solutions at five N:P supply ratios ͑1.7, 5, 15, 45, 135͒ combined with two levels of supply ͑geometric means of N and P supply͒. In experiment 2, two Carex and two grass species were grown in sand at the same five N:P supply ratios combined with three levels of supply and two light intensities ͑45% or 5% day-light͒. After 12-13 weeks of growth, plant biomass, allocation, leaf area, tissue nutrient concentrations and rates and nutrient uptake depended significantly on the N:P supply ratio, but the type and strength of the responses differed among these traits. The P concentration and the N:P ratio of shoots and roots as well as the rates of N and P uptake were mainly determined by the N:P supply ratio; they showed little or no dependence on the supply level and relatively small interspecific variation. By contrast, the N concentration, root mass ratio, leaf dry matter content and specific leaf area were only weakly related to the N:P supply ratio; they mainly depended on plant species and light, and partly on overall nutrient supply. Plant biomass was determined by all factors together. Within a level of light and nutrient supply, biomass was generally maximal ͑i.e. co-limited by N and P͒ at a N:P supply ratio of 15 or 45. All species responded in a similar way to the N:P supply ratio. In particular, the grass species Phalaris arundinacea and Molinia caerulea showed no differences in response that could clearly explain why P. arundinacea tends to invade P-rich ͑N-limited͒ sites, and M. caerulea P-limited sites. This may be due to the short duration of the experiments, which investigated growth and nutrient acquisition but not nutrient conservation. Plant Ecology ͑2005͒ 176:35-55

Stoichiometric homeostasis of vascular plants in the Inner Mongolia grassland

“…Suggestions of strong stoichiometric homeostasis were also found from field studies of wetland plants and aquatic macrophytes (Demars and Edwards, 2007). For aboveground N:P ratio, Güsewell (2004) reported H values for herbaceous plants ranging from 1.7 to 4.6 (recalculated from Shaver and Melillo 1984; Ryser and Lambers 1995;Güsewell and Bollens 2003;Güsewell 2005). These are somewhat lower than those observed in the present study for aboveground biomass of Inner Mongolia plants, which ranged from 3.08 to 14.49.…”

Why only tetraploid Solidago gigantea (Asteraceae) became invasive: a common garden comparison of ploidy levels

“…For significant interactions between treatments and ploidy level or continent, responses were calculated as reaction norms, i.e. difference between means for high and low treatment level divided by the overall mean (Güsewell 2005).…”

Time-dependent, species-specific effects of N:P stoichiometry on grassland plant growth

“…Although a high rate of P uptake by P-deficient plants is commonly observed in short-term experiments (e.g. Güsewell 2005c;Shaver and Melillo 1984), another two-year growth experiment also revealed poor nutrient recovery (i.e., percentage of nutrient accumulated in plants relative to its supply) under conditions of P-rather than N-limitation (Güsewell 2005a). Furthermore, Craine and Jackson (2009) reported a trend whereby plants grown on low-P soil do not increase biomass upon P fertilization alone, whereas those on low-N soil do increase biomass upon N fertilization, indicating a stronger inhibition of nutrient acquisition under P rather than N stress.…”

“…Short-term experiments show that adding N, leading to high N:P supply ratios, increases plant biomass, whereas adding P, leading to low N:P supply ratios, does not promote plant growth (Güsewell 2005c;Güsewell et al 2003). Longer-term experiments show contrasting results: after a period of two years, high N:P ratios reduce nutrient retention (i.e., the amount of nutrients retained in biomass), whereas low N:P ratios do not (Güsewell 2005a;Güsewell et al 2003).…”