Search Results - (Author, Cooperation:H. W. Polley)

2015-10-16

Nature Publishing Group (NPG)

0028-0836

1476-4687

Biology

Chemistry and Pharmacology

Medicine

Natural Sciences in General

Physics

*Biodiversity ; *Climate ; Climate Change/statistics & numerical data ; Conservation of Natural Resources ; Disasters/statistics & numerical data ; Droughts ; *Ecosystem ; Grassland ; Human Activities ; *Plant Physiological Phenomena

1365-3040

Blackwell Publishing Journal Backfiles 1879-2005

Biology

An investigation to determine whether stomatal acclimation to [CO2] occurred in C3/C4 grassland plants grown across a range of [CO2] (200–550 µmol mol−1) in the field was carried out. Acclimation was assessed by measuring the response of stomatal conductance (gs) to a range of intercellular CO2 (a gs–Ci curve) at each growth [CO2] in the third and fourth growing seasons of the treatment. The gs–Ci response curves for Solanum dimidiatum (C3 perennial forb) differed significantly across [CO2] treatments, suggesting that stomatal acclimation had occurred. Evidence of non–linear stomatal acclimation to [CO2] in this species was also found as maximum gs (gsmax; gs measured at the lowest Ci) increased with decreasing growth [CO2] only below 400 µmol mol−1. The substantial increase in gs at subambient [CO2] for S. dimidiatum was weakly correlated with the maximum velocity of carboxylation (Vcmax; r2 = 0·27) and was not associated with CO2 saturated photosynthesis (Amax). The response of gs to Ci did not vary with growth [CO2] in Bromus japonicus (C3 annual grass) or Bothriochloa ischaemum (C4 perennial grass), suggesting that stomatal acclimation had not occurred in these species. Stomatal density, which increased with rising [CO2] in both C3 species, was not correlated with gs. Larger stomatal size at subambient [CO2], however, may be associated with stomatal acclimation in S. dimidiatum. Incorporating stomatal acclimation into modelling studies could improve the ability to predict changes in ecosystem water fluxes and water availability with rising CO2 and to understand their magnitudes relative to the past.

Electronic Resource

1365-2486

Blackwell Publishing Journal Backfiles 1879-2005

Biology

Energy, Environment Protection, Nuclear Power Engineering

Geography

Increasing atmospheric CO2 concentrations may have a profound effect on the structure and function of plant communities. A previously grazed, central Texas grassland was exposed to a 200-µmol mol−1 to 550 µmol mol−1 CO2 gradient from March to mid-December in 1998 and 1999 using two, 60-m long, polyethylene- covered chambers built directly onto the site. One chamber was operated at subambient CO2 concentrations (200–360 µmol mol−1 daytime) and the other was regulated at superambient concentrations (360–550 µmol mol−1). Continuous CO2 gradients were maintained in each chamber by photosynthesis during the day and respiration at night. Net ecosystem CO2 flux and end-of-year biomass were measured in each of 10, 5-m long sections in each chamber. Net CO2 fluxes were maximal in late May (c. day 150) in 1998 and in late August in 1999 (c. day 240). In both years, fluxes were near zero and similar in both chambers at the beginning and end of the growing season. Average daily CO2 flux in 1998 was 13 g CO2 m−2 day−1 in the subambient chamber and 20 g CO2 m−2 day−1 in the superambient chamber; comparable averages were 15 and 26 g CO2 m−2 day−1 in 1999. Flux was positively and linearly correlated with end-of-year above-ground biomass but flux was not linearly correlated with CO2 concentration; a finding likely to be explained by inherent differences in vegetation. Because C3 plants were the dominant functional group, we adjusted average daily flux in each section by dividing the flux by the average percentage C3 cover. Adjusted fluxes were better correlated with CO2 concentration, although scatter remained. Our results indicate that after accounting for vegetation differences, CO2 flux increased linearly with CO2 concentration. This trend was more evident at subambient than superambient CO2 concentrations.

Electronic Resource

1432-1939

Biomass production ; Defoliation ; Grasslands ; Nitrogen accumulation ; Prairie dog colony

Springer Online Journal Archives 1860-2000

Biology

Summary The effects of defoliation on growth and nitrogen (N) nutrition were examined in populations of Agropyron smithii (western wheatgrass) collected from a heavily grazed black-tailed prairie dog (Cynomys ludovicianus) colony (ON-colony) and a nearby lightly grazed, uncolonized area (OFF-colony). Defoliated and nondefoliated plants were grown at low soil N availability with similar sized defoliated individuals of A. smithii from a grazing-exclosure population as a common competitor. Sequential harvests were made over 24 days following defoliation. Growth analysis plus biomass and N yield and distribution data were used to identify features which may contribute to plant defoliation tolerance. Defoliation reduced total production 34% across populations. Defoliated plants produced as much new blade tissue, but only 67% as much new root biomass as did nondefoliated controls. Plants from prairie dog colonies accumulated biomass at a faster relative rate than did plants from uncolonized sites, in part, because of a 250% greater mean relative growth rate of blades and more than 200% greater rate of biomass production per unit blade biomass. Total N accumulation was significantly greater in defoliated ON- than OFF-colony individuals. The mean relative accumulation rate of N was increased by defoliation in ON-colony plants, but reduced by defoliation in OFF-colony plants. The mean rate of N accumulation per unit root biomass was more than 300% greater in the ON- than OFF-colony population. Colony plants initially had a greater proportion of biomass and N remaining after defoliation in roots. Initial differences between populations in the distribution of biomass and N were eliminated as colony plants concentrated 24-day accumulation of biomass and N in aboveground structures. The data suggest that the combination of growth, N nutrition, and biomass and N distribution characteristics of the colony population likely confer a high rate of resource capture on heavily grazed prairie dog colonies.

Electronic Resource