Winter survival is a determinant factor for the persistence of perennials grown in northern climates. High winter survival cultivars, however, have lower yield due to their early transition into a dormant state in the fall. Here we describe a whole plant assay entirely performed indoor in growth chambers and walk-in freezers to identify low-dormant genotypes with superior freezing tolerance within populations of open pollinated species. Three successive freezing stresses are applied to a broad base of 3000 genotypes to progressively eliminate 97% of the population and to retain only the 3% best performing genotypes. This approach can be used to generate recurrently selected populations in different species.

The increase in atmospheric carbon dioxide concentration ([CO2]) and consequent increase in air temperature is expected to have significant effects on plant growth and nutritive value. Studies examining the effects of elevated [CO2] on plants under field conditions have been limited by the inherent difficulty to modify air composition in open air. Here we describe an efficient and inexpensive open‐top chamber (OTC) system designed to study the effects of elevated atmospheric [CO2] and temperature on perennial alfalfa–timothy (Medicago sativa L.)–(Phleum pratense L.) mixture. The design and construction of these OTCs are described in detail, along with cost estimation for each component. Eight OTCs, each with 1.2 m2 of ground area (four with elevated [CO2] and four with ambient [CO2]) were fabricated and four control plots of the same dimension were established to assess the chamber effects on plant responses to CO2. The [CO2] in elevated‐CO2 chambers fell 93% of the time within ±20% of the targeted 600 µmol mol−1 CO2, based on 10 min averages. The CO2 consumption in elevated‐CO2 chambers averaged 3.0 kg CO2 m−2 d−1. To ensure that the environment within OTCs was similar to the surrounding field, growing conditions were determined in all chambers and control plots. Adequate light transmission was observed compared to control plots (93%) and the temperature increase was 0.7°C on average. After two growing seasons of continued use, this system has proven its effectiveness for studying the effects of CO2 and climate change in the field at low cost.

Freezing tolerance is a determinant factor of persistence of perennials grown in northern climate. Selection for winterhardiness in field nurseries is difficult because of the unpredictability of occurrence of test winters allowing the identification of hardy genotypes. Here we describe a whole-plant assay entirely performed indoor in growth chambers and walk-in freezers to identify genotypes with superior tolerance to freezing within populations of open pollinated species. Three successive freezing stresses are applied to progressively eliminate 90 % of the population and to retain only the 10 % best performing genotypes. This approach can be used to generate recurrently selected populations more tolerant to freezing in different species.