Determination of root biomasses of three species grown in a mixture using stable isotopes of carbon and nitrogen

A method is evaluated that employs variation in stable C and N isotopes from fractionations in C and N acquisition and growth to predict root biomasses of three plant species in mixtures. Celtis laevigata Willd. (C3), Prosopis glandulosa Torr. (C3, legume) and Schizachyrium scoparium (Michx.) Nash (C4), or Gossypium hirsutum L. (C3), Glycine max (L.) Merr. (C3 legume), and Sorghum bicolor (L.) Moench (C4) were grown together in separate, three-species combinations

Woody invasion of grasslands: evidence that CO2 enrichment indirectly promotes establishment of Prosopis glandulosa

Grasslands worldwide have been invaded by woody species during the last 200 years. Atmospheric CO2 enrichment may indirectly have facilitated invasion by reducing soil water depletion by grasses

Soil- and Plant-Water Dynamics in a C3/C4 grassland exposed to a Subambient to superambient CO2 Gradient

Plants may be more sensitive to carbon dioxide (CO2) enrichment at subambient concentrations than at superambient concentrations, but field tests are lacking. We measured soil-water content and determined xylem pressure potentials and δ13C values of leaves of abundant species in a C3/C4 grassland exposed during 1997-1999 to a continuous gradient in atmospheric CO2 spanning superambient concentrations (200-560 µmol mol-1)

Yield of wheat across a subambient carbon dioxide gradient

Yields and yield components of two cultivars of day-neutral spring wheat (Triticum aestivum L.) were assessed along a gradient of daytime carbon dioxide (CO2) concentrations from about 200 to near 350 µmol CO2 (mol air)–1 in a 38 m-long controlled environment chamber. The range in CO2 concentration studied approximates that of Earth’s atmosphere since the last ice age. This 75% rise in CO2 concentration increased grain yields more than 200% under well-watered conditions and by 80–150% when wheat was grown without additions of water during the last half of the 100-day growing season. The 27% increase in CO2 from the pre-industrial level of 150 years ago (275 µmol mol–1) to near the current concentration (350 µmol mol–1) increased grain yields of ‘Yaqui 54’ and ‘Seri M82’ spring wheats by 55% and 53%, respectively, under well-watered conditions. Yield increased because of greater numbers of grains per spike, rather than heavier grains or numbers of spikes per plant. Water use increased little with CO2 concentration, resulting in improved water use efficiency as CO2 rose. Data suggest that rising CO2 concentration contributed to the substantial increase in average wheat yields in the U.S. during recent decades

Gas exchange and photosynthetic acclimation over subambient to elevated CO2 in a C3-C4 grassland

Atmospheric CO2 (Ca) has risen dramatically since preglacial times and is projected to double in the next century. As part of a 4-year study, we examined leaf gas exchange and photosynthetic acclimation in C3 and C4 plants using unique chambers that maintained a continuous Ca gradient from 200 to 550 µmol mol-1 in a natural grassland. Our goals were to characterize linear, nonlinear and threshold responses to increasing Ca from past to future Ca levels. Photosynthesis (A), stomatal conductance (gs), leaf water-use efficiency (A/gs) and leaf N content were measured in three common species: Bothriochloa ischaemum, a C4 perennial grass, Bromus japonicus, a C3 annual grass, and Solanum dimidiatum, a C3 perennial forb. Assimilation responses to internal CO2 concentrations (A/Ci curves) and photosynthetically active radiation (A/PAR curves) were also assessed, and acclimation parameters estimated from these data. Photosynthesis increased linearly with Ca in all species (P \u3c 0.05). S. dimidiatum and B. ischaemum had greater carboxylation rates for Rubisco and PEP carboxylase, respectively, at subambient than superambient Ca (P \u3c 0.05). To our knowledge, this is the first published evidence of A up-regulation at subambient Ca in the field. No species showed down-regulation at superambient Ca. Stomatal conductance generally showed curvilinear decreases with Ca in the perennial species (P \u3c 0.05), with steeper declines over subambient Ca than superambient, suggesting that plant water relations have already changed significantly with past Ca increases. Resource-use efficiency (A/gs and A/leaf N) in all species increased linearly with Ca. As both C3 and C4 plants had significant responses in A, gs, A/gs and A/leaf N to Ca enrichment, future Ca increases in this grassland may not favour C3 species as much as originally thought. Non-linear responses and acclimation to low Ca should be incorporated into mechanistic models to better predict the effects of past and present rising Ca on grassland ecosystems

California Desert Resource Inventory Using Multispectral Classification of Digitally Mosaicked Landsat Frames

Time and budget constraints have precluded the use of conventional mapping techniques for the U.S. Bureau of Land Management to produce a comprehensive resource inventory of the California deserts region as mandated by the California Desert Conservation Act. A Landsat mosaic at full resolution for ten scenes over the California deserts region was used to provide a continuous data base for multispectral thematic classification. Procedures for adjustment of brightness values between frames and the digital mosaicking of the Landsat frames to standard map projections were developed for this task and are discussed. The principle of transect sampling was adopted as a means to obtain a uniform classification throughout the entire desert while generating one set of classification statistics. The transects were selected by the BLM science team to include all variable types in the landscape. The initial set of unsupervised statistical clusters was reduced by the BLM staff to 100 primary statistical clusters and applied to twelve small (512×512) test areas extracted from the Landsat mosaic. Subsequent to verification, classification was performed on the entire desert mosaic in 1°× 1° segments. Resource class assignment was aided by including, in a post classification procedure, DMA/NCIC digital terrain elevation data (with derived measures of slope gradient and aspect) registered to the Landsat mosaic. The combination of local terrain variations and a global sampling strategy based on transects provided the framework for an accurate classification throughout the entire desert region

Increasing CO2 from subambient to elevated concentrations increases grassland respiration per unit of net carbon fixation

Respiration (carbon efflux) by terrestrial ecosystems is a major component of the global carbon (C) cycle, but the response of C efflux to atmospheric CO2 enrichment remains uncertain. Respiration may respond directly to an increase in the availability of C substrates at high CO2, but also may be affected indirectly by a CO2-mediated alteration in the amount by which respiration changes per unit of change in temperature or C uptake (sensitivity of respiration to temperature or C uptake)