Showing papers by "Sven Jonasson published in 1997"

Effects of labile soil carbon on nutrient partitioning between an arctic graminoid and microbes

Abstract: We measured partitioning of N and P uptake between soil microorganisms and potted Festuca vivipara in soil from a subarctic heath in response to factorial addition of three levels of labile carbon (glucose) combined with two levels of inorganic N and P. The glucose was added to either non-sterilized or sterilized (autoclaved) soils in quantities which were within the range of reported, naturally occurring amounts of C released periodically from the plant canopy. The aims were, firstly, to examine whether the glucose stimulated microbial nutrient uptake to the extent of reducing plant nutrient uptake. This is expected in nutrient-deficient soils if microbes and plants compete for the same nutrients. Secondly, we wanted to test our earlier␣interpretation that growth reduction observed in graminoids after addition of leaf extracts could be caused directly by labile carbon addition, rather than by phytotoxins in the extracts. Addition of high amounts of N did not affect the microbial N pool, whereas high amounts of added P significantly increased the microbial P pool, indicating a luxury P uptake in the microbes. Both plant N and in particular P uptake increased strongly in response to soil sterilization and to addition of extra N or P. The increased␣uptake led to enhanced plant growth when both elements were applied in high amounts, but only led to increased tissue concentrations without growth responses when the nutrients were added separately. Glucose had strong and contrasting effects on plant and microbial N and P uptake. Microbial N and P uptake increased, soil inorganic N and P concentrations were reduced and plant N and P uptake declined when glucose was added. The responses were dose-dependent within the range of 0–450 μg C g−1 soil added to the non-sterilized soil. The opposite responses of plants and microbes showed that plant acquisition of limiting nutrients is dependent on release of nutrients from the soil microbes, which is under strong regulation by the availability and microbial uptake of labile C. Hence, we conclude, firstly, that the microbial populations can compete efficiently with plants for nutrients to an extent of affecting plant growth when the microbial access to labile carbon is high in nutrient deficient soils. We also conclude that reduced growth of plants after addition of leaf extracts to soil can be caused by carbon-induced shifts in nutrient partitioning between plants and microbes, and not necessarily by phytotoxins added with the extracts as suggested by some experiments.

Effects of shading, nutrient application and warming on leaf growth and shoot densities of dwarf shrubs in two arctic-alpine plant communities.

Abstract: Responses in shoot growth and activation of new meristems of dominant dwarf shrubs were measured after six years of shading or temperature enhancement with and without NPK fertilizer addition to a

Carbon dioxide and methane exchange of a subarctic heath in response to climate change related environmental manipulations.

Abstract: Responses of CO 2 and CH 4 exchange to NPK fertilization, soil warming and shading were investigated at a tree line heath site near Abisko in subarctic Sweden. Respiration increased with fertilization and decreased with shading after seven yr of treatment. Warming caused small overall changes in respiration. Photosynthesis was stimulated by fertilizer application to an extent which exceeded the increase in respiration and hence caused the system to increase its atmospheric CO 2 sink strength. Warming, on the contrary, tended to increase the CO 2 efflux from the ecosystem. Shading caused no significant net change in carbon flux but a significant reduction in the carbon turnover rate. Significant CH4 consumption rates suggested that subarctic heath systems may constitute a significant sink for atmospheric CH 4 . Inorganic nitrogen fertilization increased CH 4 consumption which was unexpected since N addition normally inhibits CH 4 consumption rates in natural and arable ecosystems. As expected from the relatively weak temperature dependency of microbial CH 4 oxidation reported in previous studies, warming caused no increase in CH 4 consumption rates..

Elevated atmospheric CO2 affects decomposition of Festuca vivipara (L.) Sm. litter and roots in experiments simulating environmental change in two contrasting arctic ecosystems

Abstract: Elevated atmospheric CO2 affects decomposition of Festuca vivipara (L. ) Sm. litter and roots in experiments simulating environmental change in two contrasting arctic ecosystems.

Variation in leaf longevity of Pistacia lentiscus and its relationship to sex and drought stress inferred from leaf δ13C

Abstract: 1. Leaf formation, loss, retention, longevity and biomass on male branches of the evergreen mediterranean shrub Pistacia lentiscus, L. correlated strongly with water-use efficiency inferred from leaf δ13C across a gradient of precipitation on the island of Mallorca, Spain. 2. The correlations suggest that the leaf phenology is under control of drought-induced constraints on the carbon balance. 3. In fruiting female branches, the correlations between the inferred water-use efficiency and number of formed and retained leaves, leaf biomass and leaf longevity were non-significant. Leaf formation was strongly reduced by fruiting and the females compensated the reduced photosynthetic capacity by retaining older leaves for a longer time than male plants. 4. It is suggested that leaf longevity in females is under strong control of resource allocation to fruit formation which is ‘overlaid’ on the drought-induced carbon stress, which led to the observed longer leaf longevity in females than in males.

Effects on plant production after addition of labile carbon to arctic/alpine soils.

Abstract: Biomass production was analysed in Festuca vivipara, grown for 3 months in pots with non-sterilized or sterilized soil after factorial addition of three levels of labile carbon combined with high and low levels of N and P. The soil was a nutrient-poor subarctic heath soil. In the non-sterilized soil plant biomass production increased strongly only in the treatment with high levels of both N and P, which suggests that both nutrients limited plant growth. In the sterilized soil addition of a high level of N without P addition gave almost the same growth response as in the combined NP treatment. This was because of a more than 30-fold increase of inorganic phosphorus in the soil as P was released from the killed microbial biomass after sterilization. Sugar addition reduced plant growth in all treatments. The reduction in plant growth was dose dependent within the range of 0–450 μg C g−1 soil added to the non-sterilized soil, but the response levelled off at 233 μg C g−1 soil in the soil that had been sterilized at the start of the experiment. The plant response, together with observed depletion of soil inorganic N and P, indicated that the microbial biomass immobilized nutrients efficiently and reduced plant growth when extra labile carbon was added. The inhibition of growth was lower, however, in the soil which had been sterilized, probably because of a slow recovery of the microbial populations in it. Two of the nutrient-carbon solutions closely matched the N, P and C concentrations in a solution containing leaf extracts of Cassiope tetragona and Betula tortuosa that had been used previously to test for possible allelopathic effects of compounds in the leaf extracts. These extracts also reduced plant growth. The growth reduction was equally large or larger after nutrient-sugar addition than after addition of leaf extracts in three out of the four possible combinations of species and sterilized or non-sterilized soil. In the fourth case (Betula extract added to sterilized soil), the effect was larger when leaf extract was added than after addition of the nutrient-carbon solution. This could be due to a low rate of microbial degradation of phytotoxic substances in this soil because of a slow recovery of the microbial populations after sterilization. The generally stronger or equal effect of the nutrient-sugar addition compared to the leaf extract addition leads to the conclusion that microbial nutrient immobilization and microbial competition for nutrients increased as a function of labile carbon addition with the extract. Hence, it appears that enhanced microbial activity and microbial nutrient immobilization rather than phytotoxic effects was the primary reasons for the reduced biomass production in F. vivipara even after addition of the leaf extracts.