Soil compaction effects on water status of ponderosa pine assessed through 13C/12C composition

Soil compaction is a side effect of forest reestablishment practices resulting from use of heavy equipment and site preparation. Soil compaction often alters soil properties resulting in changes in plant-available water. The use of pressure chamber methods to assess plant water stress has two drawbacks: (1) the measurements are not integrative; and (2) the method is difficult to apply extensively to establish seasonal soil water status. We evaluated leaf carbon isotopic composition (delta(13)C) as a means of assessing effects of soil compaction on water status and growth of young ponderosa pine (Pinus ponderosa var. ponderosa Dougl. ex Laws) stands across a range of soil textures. Leaf delta(13)C in cellulose and whole foliar tissue were highly correlated. Leaf delta(13)C in both whole tissue and cellulose (holocellulose) was up to 1.0parts per thousand lower in trees growing in non-compacted (NC) loam or clay soils than in compacted (SC) loam or clay soils. Soil compaction had the opposite effect on leaf delta(13)C in trees growing on sandy loam soil, indicating that compaction increased water availability in this soil type. Tree growth response to compaction also varied with soil texture, with no effect, a negative effect and a positive effect as a result of compaction of loam, clay and sandy loam soils, respectively. There was a significant correlation between C-13 signature and tree growth along the range of soil textures. Leaf delta(13)C trends were correlated with midday stem water potentials. We conclude that leaf delta(13)C can be used to measure retrospective water status and to assess the impact of site preparation on tree growth. The advantage of the leaf delta(13)C approach is that it provides an integrative assessment of past water status in different aged leaves.