Moderate Herbivory Promotes the Growth and Photosynthesis of Replanted Calligonum caput-medusae Saplings along the Tarim River

Herbivory can cause ecological, morphological, and physiological responses in plants. The effects of herbivory on plants vary significantly for the differences of water, light and nitrogen resources of plants.

The desert riparian forest ecosystem along the Tarim River in northwest China contains a relatively high biodiversity of plants and animals. However, due to changes induced by global climate change and by increased disturbances by human activities during the last five decades, plant communities have been seriously degraded. Calligonum caput-medusae is a replanted species along the Tarim River. Although restoration zones were fenced, C. caput-medusae saplings are facing short-term and frequent herbivory by goats belonging to poor shepherds who reside inside of the restoration zones, during the period of food shortage in spring. The replanted saplings respond to herbivory in different ways.

To determine the effects of herbivory on C. caput-medusae saplings along the Tarim River, and provide information to aid in the management of ecological restoration zones in this arid region and support practical guidelines for the amount of shrub shoots to remove in the restoration zone used as forage in spring, ZHU Chenggang et al. simulated herbivory with clipping to test two hypotheses. They hypothesized that moderate herbivory may positively affect replanted shrub saplings due to overcompensatory growth and compensatory photosynthesis, and high amounts of defoliation may change water availability and impair photosynthesis and growth of saplings. They applied four defoliation treatments (0%, 30%, 50% and 70%) to 2-year-old C. caput-medusae saplings to test the effects of herbivory on C. caput-medusae saplings.

According to the results, moderately defoliated (about 30%) saplings grew faster and had higher photosynthetic performance than controls. However, defoliation of 50% or more reduced growth due to undercompensatory photosynthesis and reduced water availability. Nonphotochemical quenching by thermal dissipation provided photoprotection when absorbed light energy used in Photosystem II (PSII) photochemistry was inhibited, reducing excess excitation energy and allowing saplings with high amounts of defoliation to maintain adequate photosystem functioning.

The results suggested that moderate herbivory of replanted shrubs used as forage in arid ecological restoration projects is feasible, but that uncontrolled grazing should be forbidden. The study was published in Plant Ecology in February 2014.