Effects of carbon dioxide, water and nutrient fluxes on loblolly pine (Pinus taeda L.)

Scope and method of study. A field study was established in southeast Oklahoma in 1993. The objective of this study was to determine the extent to which elevated carbon dioxide, water and nutrients affect the seasonal and long-term differences in light-saturated rate of photosynthesis {dollar}rm(Psb{lcub}max{rcub}),{dollar} maximum stomatal conductance to water vapor {dollar}rm(Gsb{lcub}max{rcub}){dollar} and total chlorophyll content in loblolly pine. The needles were also tested for acclimation to elevated concentrations of carbon dioxide. Main plot treatments were (1) control, (2) fertilized, (3) irrigated and (4) irrigated & fertilized. Sub plot treatments were three levels of carbon dioxide at (1) ambient, (2) ambient +175 {dollar}rmmu l lsp{lcub}-1{rcub}{dollar} and (3) ambient +350 {dollar}rmmu l lsp{lcub}-1{rcub}.{dollar} Selected branches were fumigated for 24 hrs/day throughout the study, using branch chamber technology. {dollar}rm (Psb{lcub}max{rcub}), (Gsb{lcub}max{rcub}){dollar} and total chlorophyll content were obtained monthly from June 1994 to March 1996. A/C{dollar}rmsb{lcub}i{rcub}{dollar} curves were developed twice during the study to test for acclimation of foliage to elevated concentrations of carbon dioxide. The main effects of carbon dioxide, water and nutrient fluxes on {dollar}rm(Psb{lcub}max{rcub}), (Gsb{lcub}max{rcub}){dollar} and total chlorophyll content were analyzed using the standard split plot analysis. A/C{dollar}rmsb{lcub}i{rcub}{dollar} curves were fitted to an empirical non-linear regression model and analyzed.; Findings and conclusions. {dollar}rm Psb{lcub}max{rcub}{dollar} was approximately 70% and 100% greater for 525 and 700 {dollar}rmmu l lsp{lcub}-1{rcub}{dollar} treated branches, respectively compared to the 350 {dollar}rmmu l lsp{lcub}-1{rcub}{dollar} treated branches for the whole study period for one-year old needles. P{dollar}rmsb{lcub}max{rcub}{dollar} was approximately 35% and 65% greater for the 525 and 700 {dollar}rmmu l lsp{lcub}-1{rcub}{dollar} treated branches, respectively compared to 350 {dollar}rmmu l lsp{lcub}-1{rcub}{dollar} treated branches for the whole study period for the current-year needles. {dollar}rm Gsb{lcub}max{rcub}{dollar} and total chlorophyll content were not affected by elevated carbon dioxide concentrations. {dollar}rm Psb{lcub}max{rcub}, Gsb{lcub}max{rcub}{dollar} and total chlorophyll content were not affected by irrigation and fertilization treatments. The results from the A/C{dollar}rmsb{lcub}i{rcub}{dollar} curves indicated a negative acclimation in 7 of 12 trees due to the limitations imposed by RuBP regeneration capacity or inorganic phosphate regeneration capacity or the enzyme kinetics of rubisco. It is unlikely that the phenomenon of acclimation found in this study was based on either nutrient limitation or available soil volume for the growth of roots.