Browsing by Subject "species richness"

Pollinator abundance and diversity are declining at an alarming rate around the world, which poses a threat to ecosystem stability and human wellbeing. There are signs that growing pollination deficits are limiting agricultural yields in Finland and globally. More information is urgently needed on how changes in pollinator communities affect crop yields and how adequate pollination services could be achieved across a range of crops and locations. This study explores the effects of pollinator abundance and diversity on caraway (Carum carvi L.) pollination and yield. Caraway is partly wind-pollinated, but insect pollination has been shown to increase its yield. Flower visits of pollinating insects were monitored on 30 caraway fields in southern Finland in summer 2019. Yield samples were collected from open-pollinated plants and from control plants excluded from pollinators. Pollinator exclusion reduced caraway fruit set by 13.2% and seed yield by 39.6%. Fruit set, 100-seed weight and seed yield increased with increasing flower visitation. Pollinator species richness and Shannon index had no significant effect on the yield components, but evenness of the pollinator community had a negative effect on seed yield and the numbers of umbels and umbellets in the caraway plants. The most abundant pollinators visiting caraway were syrphid flies, non-syrphid Diptera and honeybees. Visits by syrphid flies and honeybees increased seed yield, while visits by non-syrphid Diptera, solitary bees and Lepidoptera had no significant effect on the yield components. Flower visits by beetles reduced 100-seed weight. The results show that syrphid flies provide an important pollinator service for caraway cultivation. It would be beneficial to study which syrphid fly species are the most effective pollinators for caraway and how to manage fields and farmland landscapes to increase their numbers. Relying only on managed honeybees to enhance caraway pollination may not be advisable due to their potential negative effects on wild pollinators. While increased pollinator diversity did not improve caraway pollination or yield in this one-season study, it may be important for the stability of pollinator services in long term.

Improving land management to mitigate climate change is important, especially in agriculture on soils with high organic content. Many studies have found evidence that increasing diversity can help to improve plant biomass production and soil carbon storage. This is attributed to complementarity which consists of more efficient resource use due to niche differences and facilitative interactions. For the total climate impact, the effect of greenhouse gas emissions from the soil needs to be considered. To find out if adding more species to a grass mixture could have similar benefits in boreal zone grass cultivation in Finland, an experiment was set up with four different species mixtures, and three levels of species richness were established under a nurse crop. It was additionally of interest if these effects can counter the emissions of cultivation on organic soils. Biomass samples were collected both before the nurse crop was removed and at the end of the growing season. Both species richness and Shannon diversity index were considered as explanatory factors. Carbon exchange, divided into respiration and photosynthetic capacity, as well as nitrous oxide and methane fluxes, were monitored monthly. There was no strong evidence that species richness affects biomass or greenhouse gas fluxes during the first year. The effect of species richness on the biomass was clearer when the diversity index was considered. These results were significant when the lowest biomass values were excluded from the analysis, probably because complementary resource use needs enough biomass to have an effect. The differences in carbon flux measurements may be sensitive to timing within the growing season since the results closest to significant were obtained at the start of the season. At the time, the measurement conditions were good and the nurse crop biomass was small enough not to obscure the effects of grass mixture. When it comes to other greenhouse gases, species richness had most impact on early nitrous oxide emissions, while methane flux probably needs significantly more time for any changes to appear. Overall, the effect of species richness needs to be studied over the full grass cultivation cycle to find out the full effect. Based on current results, increasing species richness may be an option when other methods cannot be used to reduce emissions and improve carbon sink of agriculture.