Growth strategies as determinants of CO2 sequestration and response to nitrogen fertilisation in C4 grasses in South American natural grasslands

Abstract

Grass species grown in South American natural grasslands present different growth strategies related to variations in specific leaf area (SLA), leaf dry matter content (LDMC) and possible nitrogen (N) allocation. Nitrogen fertilisation can have effects on physiological processes such as CO2 assimilation; however, these responses can change depending on the growth strategy adopted by each species. The aim of the present study is to determine the effects of N fertilisation on SLA, LDMC and CO2 assimilation in eight C4 grass species: Axonopus affinis, Paspalum pumilum, P. notatum, P. urvillei, P. plicatulum, Andropogon lateralis, Saccharum angustifolium and Aristida laevis. These species were cultivated in pots filled with soil subjected to two conditions of N availability: nil (control) and 200 mg N kg–1 soil. The SLA of Axonopus affinis was 5.4 times higher than that of Aristida laevis. Axonopus affinis and P. pumilum recorded the lowest LDMC, their leaves showed 53% lower LDMC than observed for Aristida laevis, on average. Resource-capture species showed variation in leaf area with N addition to values 20% higher than the control, whereas species characterised by a resource-conservation growth strategy recorded variation in leaf area with N addition to values only 8% higher than the control. With N addition, the CO2 assimilation of resource-capture species represented variation (increase) nine times that of resource-conservation species compared with their respective controls. Resource-capture species have greater CO2 capture potential than resource-conservation species, mainly a result of N addition.

Phosphate sources affect P and N nutrition in pluri-specific natural grasslands in the Brazilian Pampa biome

“…For example, P. notatum in all three treatments was the species with the highest dry matter production and the highest P absorption per hectare. These observations corroborate the fact that this species, along with other species of this genus, such as P. pumilum, P. urvillei and, P. plicatulum, had high P use efficiency in leaves and roots for dry matter production (Marques et al, 2020b). However, D. sabulorum and E. uliginosa had the highest P concentration in the biomass, probably due to very efficient strategies of P uptake, but with low efficiency in the use to produce plant biomass.…”

“…Applying P to the naturally P-poor soil of the Pampa native grasslands can change the botanical composition due to the differences mentioned above of each plant species in acquiring and using nutrients in that environment. The functional group species specialized in capturing P may have higher rates of relative growth and higher responses to P application, whereas the functional group specialist in saving resources may have a low response to P application (Oliveira et al, 2014;Marques et al, 2020b). This hypothesis was confirmed by the contrast in the growth patterns of the species E. uliginosa (grew more in the SP treatment) and D. sabulorum (grew more in the control).…”